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KurtV
08-16-2006, 09:25 PM
Theory: SWGs are generally placed on higher-end pools that are more likely to have other high-end features such as water falls, sheer descents, laminar jets, fountains, and other sources of aeration. That aeration, rather than the SWG itself, is the cause of the rising pH (or at least a contributor).

Discussion: We know, at least anecdotally, that many, but by no means all, SWG pool owners experience a constantly rising pH that has to be counteracted with acid. Most people seem to believe that there's a causal relationship between the SWG and the rising pH but I've never seen an explanation of why this might be so. Since not every SWG pool fights constantly rising pH, couldn't some other feature that's common on pools with SWGs actually be the cause? (Correllation is a long way from causation.) As we all know from Ben's Alkalinity Lowering Procedures, aeration of pool water will cause high pH to rise. Therefore, I theorize that the aerating features are a likely cause of rising pH. (I have no idea if such features are more common on SWG-equipped pools but it seems logical.)

My (very limited) basis for this theory is that I also have a constantly rising pH in my pool but no SWG. I do, however, have a negative edge on my pool that I try to run daily and which provides a great deal of aeration. From the alkalinity education I've been receiving from Ben, Richard, and Evan, I know that the out-gassing this aeration induces certainly doesn't help my pH situation and may indeed account for much, if not all, of the pH rise I see. Do others with like water features, with or without SWGs, see the same kind of upward trend in pH?

Discuss among yourselves (or ignore this if I'm all wet).

By the way, I'm not looking for any help with my own situation here. It's manageable with 16 to 24 oz. of muriatic acid per day and I'm trying to collect a month's worth of good data before I ask.

Phillbo
08-16-2006, 09:44 PM
I'm not looking for any help with my own situation here. It's manageable with 16 to 24 oz. of muriatic acid per day and I'm trying to collect a month's worth of good data before I ask.


thats a lot of acid .. I use that in a week. At most.

I test weekly and could not imagine having to make sure I make it home to test and add chemicals daily..

gwrace1
08-16-2006, 10:03 PM
I run my SWG on a 26000 gallon above ground pool. It does a great job of maintaining the chlorine level. However I do have to add acid once per week to keep PH under control. I do have two returns on the pool managed by a three way valve. One operates the Aqualumiator/fountain pool light and the other runs a PoolSkim ahead of the skimmer. I really don't have any aeration going other than when we rarely run the fountain to cool down the water.

I've read somewhere of the chemical process that goes on that seems to explain the rise in PH. We are on a very alkaline south Texas well so all my fill water helps to contribute to that PH rise as well.

chem geek
08-16-2006, 10:24 PM
Could y'all post your TA and pH numbers (your "target" pH you reach after adding acid and your "high" pH at the point you need to add acid). And also compare your readings against this chart (http://richardfalk.home.comcast.net/pool/CO2.htm). Though it is absolutely true that increased aeration will cause an increased outgassing of carbon dioxide and subsequent rise in pH (and therefore acid demand), it is also possible that some of you may be at too high a TA level anyway.

The easiest solution, at any aeration rate, is to lower your TA so you get into the "green" range on the aforementioned chart (some can be in the "orange" range, but this is dependent on aeration). My coloring of the chart is just based on experience from users so far and is subject to change, which is why I'm interested in your results.

Richard

KurtV
08-16-2006, 10:58 PM
Richard,
I hadn't intended this thread to focus too specifically on my situation but here's the last three weeks or so of my testing (CYA 30 ppm and calcium hardness 220 ppm throughout this period, daytime water temperature between 89 and 92 deg F, about 2800 ppm salt but no SWG):

Date pH Alk. Acid addition
7/26 7.8 100 24 oz.
7/27 7.4 100
7/28 7.8 100 16 oz.
7/29 7.7 100 16 oz.
7/30 7.2 90 32 oz. (before testing)
7/31 Vacation
8/1 Vacation 16 oz.
8/2 Vacation
8/3 Vacation 16 oz.
8/4 7.8 90 28 oz.
8/5 7.6 80 16 oz.
8/6 7.6 80 16 oz.
8/7 7.4 80 8 oz.
8/8 7.6 70 16 oz.
8/9 7.6 70 16 oz.
8/10 7.5 70 16 oz.
8/11 7.3 70 8 oz.
8/12 7.4 70 16 oz.
8/13 7.6 70 16 oz.
8/14 Work trip
8/15 7.6 70 16 oz.
8/16 7.6 70 24 oz.

Sorry about the format, couldn't get it any better than this.

Phillbo
08-16-2006, 11:04 PM
3 days ago .. TA = 95. I add acid once a week and the pH is normaly around 7.8 ish when tested weekly. I don't test every time. just add based on past experience.

DavidD
08-16-2006, 11:19 PM
Kurt,

Just for comparison & discussion, I have a waterfall and two spa jets (lots of bubbles). I pretty much turn the water fall on and the spa jets always put out some bubbles any time the pump is running. Both features can be independently shut off but we rarely do. I have three returns that are always pointed up as the wife likes the “ripples”. PH is consistently in the 7.5 range and Alk around 110. I may have added 16 oz. of muratic acid since April and I would believe that my pool is at least in the mid to upper realm of high aeration. 16K Fiberglass in ground pool, CH is 150, CYA 40 and FC stays between 2 and 5. I do have 3200 ppm of Salt, no SWC, 1 HP Superpump & DE filter.

Dave

KurtV
08-16-2006, 11:24 PM
David,
As that doesn't support my theory at all, we'll have to throw it out as a bogus data point.:D

(Hey, it's just a theory.)

chem geek
08-17-2006, 12:18 AM
Well Kurt's data shows that it is definitely the outgassing of carbon dioxide that is going on, at least initially. If the SWCG system were somehow introducing base into the pool, then that would increase pH and TA such that adding acid would get you right back where you started with pH and TA. Instead, Kurt's data shows a steady decline in TA at the same "target" pH.

Interestingly, Kurt should be seeing a slow down in the amount of pH rise and acid demand as his TA is lowered, but I don't see that from the data. He is also now in the "green" region though still out of equilibrium with over 5 times as much carbon dioxide dissolved in the water as is found in air. If he reaches a state where his TA does not seem to be lowering (and it looks like this may now be the case, or close to it), but he still needs to add acid, then something in the SWCG system is indeed adding base (and was earlier too, but was masked by the CO2 outgassing).

There are several ways that an SWCG system can add base. The simplest is having the generated chlorine gas not dissolve completely into the water since the conversion of chlorine gas into HOCl is a highly acidic process that partly compensates for the highly basic process of hydrogen gas production. The difficulty in detecting this is that you will find bubbles of hydrogen gas flowing from the salt cell into your pool and you can't easily tell the difference between hydrogen gas and chlorine gas except possibly a smell of "fresh" chlorine.

Great data collection Kurt! Keep it up.:)

Richard

mas985
08-17-2006, 12:18 AM
I thought the rising PH was due to the chemical reactions of the SWG as indicated here: http://www.goldlinecontrols.com/ElectronicChlorination.aspx

The hydroxide ions on the cathod increase the pool water PH.

As for my experience, I have no water features at all and my PH can go from 7.2 to 7.8 in less than a week.

One other thing not mentioned which could have a significant effect is that fill water, such as mine, can be quite basic. Mine is over 7.8 in PH.

waterbear
08-17-2006, 02:19 AM
You all might be interested with the thread I started in the china shop called "the great tetraborate experiment". I have a SWG, many water features, and since I have added 50 ppm borates to my water I have been exerpiencing less problems with pH rising as quickly. The experiment is only in it's third week but so far has indicated that the extra buffering system introduced into the water by the borax does help stabilize the pH and might require less acid over the long haul.

chem geek
08-17-2006, 02:45 AM
I thought the rising PH was due to the chemical reactions of the SWG as indicated here: http://www.goldlinecontrols.com/ElectronicChlorination.aspx

You are correct that the generation of hypochlorous acid from the SWCG is a basic (increasing pH) reaction and is equivalent to adding sodium hypochlorite to your pool, except without the sodium (chloride ion is removed instead so there is no net charge difference). However, the chlorine gets used up mostly through the breakdown from sunlight (UV) and some from the disinfection and oxidation of organics and ammonia. The net equation for the entire process is first

2Cl- + 2H2O --> Cl2(g) + H2(g) + 2OH- --> HOCl + Cl- + H2(g) + OH-
so the net of this is
Cl- + 2H2O --> HOCl + H2(g) + OH-

which is the basic (increasing pH) process you are referring to, though HOCl is a weak acid so this is weakly basic overall. Then the using up of chlorine produces the following:

2HOCl + (UV) --> O2(g) + 2H+ + 2Cl-
-or- 3HOCl + 2NH3 --> N2(g) + 3H2O + 3H+ + 3Cl-

These are weakly acidic processes since HOCl is a weak acid so using it up results in the following reaction to keep HOCl and OCl- in balance:

OCl- + H+ --> HOCl

The net reaction for the production and destruction of chlorine is:

2H2O --> 2H2(g) + O2(g)
-or-
2NH3 + 3H2O --> N2(g) + 3H2(g)

Details of all of this may be found at this thread (http://www.poolforum.com/pf2/showpost.php?p=27573&postcount=12).

This is why using chlorine bleach with a pH of 11 does not cause a rise in pH over time (nor using chlorinating liquid with a pH of 13 though there is some extra base added in this case for stability so this will increase pH a little bit). This is also why using Di-Chlor (1% solution is 6.8) in fact lowers the pH more than one would think and why Tri-Chlor (1% solution is pH 2.8) is even worse (more acidic) that it first appears.

Now if you were to build up combined chlorine such as chlorinated organic compounds that didn't fully oxidize, then yes you would lose the "acid" part of the balance and rise in pH, but I assume your CC is staying near 0.

mas985, I'm curious. What is your current TA? If it's not unusually high, then indeed something in the SWCG systems would seem to be generating more base than it should. Is your SWCG in clear plastic so that the plates are visible to you? If so, can you see gas being generated vigorously at both plates or is it mostly just at one plate (hydrogen) therefore indicating an efficient dissolving of chlorine gas in water. If you find gas bubbles on both plates and that they seem to stream off of both plates without dissolving, then the salt cell is not operating very well in dissolving the chlorine gas into the water. Some of the gas on the chlorine side could be oxygen gas (a competing reaction), but mostly it should be chlorine gas if designed correctly. When oxygen gas is produced, there is no net change in pH which is why I think the culprit is undissolved chlorine gas.

There is also an increase in outgassing of chlorine gas in salt pools, but with the high CYA and relatively low 3-5 ppm chlorine levels, the rise in pH over a week shouldn't be as high as what you and others are seeing (it's about a 0.1 rise in pH over a week). Now hot tubs are an entirely different matter where there is lots of aeration and the temperature is a lot hotter, but they also are typically covered most of the time. Lots of variables, lots of questions, and we may never find the answers, but we can try.:)

Richard

chem geek
08-17-2006, 03:02 AM
The experiment is only in it's third week but so far has indicated that the extra buffering system introduced into the water by the borax does help stabilize the pH and might require less acid over the long haul.
Evan (waterbear),

I agree that the borax helps stabilize the pH, but it won't change how much acid you need to add. Only finding the source of the "extra base" and reducing that reaction will reduce the amount of acid you need to add. We just don't know yet how much is due to carbon dioxide outgassing (which causes TA to drop when you add acid to maintain pH) and how much is due to inefficient SWCG production with outgassing of chlorine gas or some other process.

Anyway, we'll eventually sort this all out -- or not!

Richard

mas985
08-17-2006, 12:32 PM
mas985, I'm curious. What is your current TA?

100 to 110 ppm

If it's not unusually high, then indeed something in the SWCG systems would seem to be generating more base than it should. Is your SWCG in clear plastic so that the plates are visible to you?

Unfortunately not


One more thing besides the fill water being high in PH is that the pool is only 1 year old which may still affect the PH.

dawndenise
08-17-2006, 02:04 PM
Still looking for data? Pool is not quite 3 months old and pH is quite comfortable at 7.5. I add muriatic acid only when the color gets a slight pinkish tinge to it, rather than waiting for it to go up to the next #. Am only in my 3rd gallon of MA since pool filling. My target is always 7.5, since that's where my pool has "said" it's comfortable. Who am I to argue?:D

SWG online for about 2-3 weeks now. Add acid about every 10 days thus far; no appreciable change since the SWG became operational. Waterfall on 12 hours per day.

TA=80, CH=220, CYA=45, FC=5-9 range, salt=3400; generator set at 60% for 12 hours; water temps 84-89.

Fill water is very high ph (over 8), low in calcium hardness (50-ish), about 70 in alkalinity.

I just can't bring myself to drop my FC into the 1-3 range, increasing my CYA into the 60-80 range, as per SWG's recommendations. :o

chem geek
08-19-2006, 02:18 PM
Am only in my 3rd gallon of MA since pool filling.
Just wondering. Do you have any water features (waterfalls, etc.) or would you say that your pool doesn't have much aeration? What brand of SWG system are you using? Do you use a pool cover and is it opaque or a clear "solar" cover?

Since you aren't seeing the same sort of pH rise that others see in SWG pools, I'm just trying to figure out what's different about your pool.

Richard

chem geek
08-19-2006, 02:30 PM
One more thing besides the fill water being high in PH is that the pool is only 1 year old which may still affect the PH.
Yeah, I had forgotten about the effect of curing concrete in new pools. This process produces calcium hydroxide, Ca(OH)2, and is highly alkaline. In fact, for every 1 ppm of calcium hardness added to your pool during the curing process, the pH would rise by 0.08 and is equivalent (for pH) to adding 10.7 ounces of Borax to your pool.

Richard

Katy-Texas
08-19-2006, 05:43 PM
I add almost 1 USG per week to our 26,000 USG SW pool here in Houston every week in summer and 1/2 that in winter. Pool is currently 92 F :D and have 2 HP pump circ 20 hours per day of which about 1/3 (guesstimate) goes into spa and then to pool via a cascading face to the spa, about a 1 foot drop.

Silly question, muriatic acid = HCl equals H & Cl, when HCl is used, does it liberate the Cl, I side benefit is that it chlorinates pool, if so then I'll add my HCl after party as a sort of ph & shock all in one.

waterbear
08-19-2006, 06:00 PM
no,, when the HCL is added to the pool it forms hydrogen ions and cloride ions. The chloride ions combine with sodium ions in the water to form salt.

PatL34
08-19-2006, 11:24 PM
I defer to Richard in the chemistry involved in a SWCG operation, but I did a writeup in the thread mentioned in my signature, which was simplified for the newbies with SWCGs.

I do know that the pH tended to rise before and after I installed the SWCG 8 years ago. The rise is not pronounced as it used to be, as I was maintaining a 5 - 6 ppm chlorine range from algae that occured in the old Diamond Brite plaster.

With the new plaster which is still curing, I am adding a pint of muriatic acid every three days and holding 7.4 - 7.6 pH with hardly any bather load.

One has to remember after all the chemistry that Richard and I have mentioned whether by bleach or SWCG, the net result is an increase in caustic soda (NaOH), which has to be converted back to salt with muriatic acid.

This is my interpretation and Richard can chip in and correct if necessary.

Pat

chem geek
08-20-2006, 03:26 AM
Pat,

You do a very good job explaining the chemistry in simpler terms for people to understand. Thank you for doing that. There are a couple of corrections to what you wrote in your thread, but they don't detract from the main points too much except that it is not true that the production AND consumption are an alkaline (basic) process because they are not -- the net of the two (production and consumption) are neutral in pH.

The products from electrolysis are only Hydrogen (H2) gas and Chlorine (Cl2) gas. There is no sodium (Na+) produced nor consumed by this process. There are also no hydroxide ions (OH-) directly produced from the process, but because hydrogen ions (H+) are consumed and due to the balance of the two with water, the net effect is as if hydroxide ions are created (from water).

2H+ + 2e- --> H2(g)
2Cl- --> Cl2(g) + 2e-
Cl2(g) + H2O --> HOCl + H+ + Cl-
H2O --> H+ + OH-
----------------------------------------
Cl- + 2H2O --> H2(g) + HOCl + OH-

Now compare the above with introducing liquid chlorine into the water:

NaOCl + H2O --> Na+ + HOCl + OH-

You can see that both process result in the same "HOCl + OH-" and therefore have the same slightly alkaline (basic) effect on pH. The effect is not strong because HOCl is a weak acid that partly counteracts the OH- (so some product is OCl- + H2O).

If we just stopped here, then one would conclude that both the SWCG process and adding liquid chlorine cause a rise in pH and though that is true, it is not the whole story. The chlorine doesn't just keep growing and growing in concentration in the pool. Instead, it gets used up. There are several processes that use up chlorine and I list some of these in this post (http://www.poolforum.com/pf2/showpost.php?p=27573&postcount=12), but the net result is that these processes do the following:

2HOCl --> O2(g) + 2H+ + 2Cl-
2OCl- --> O2(g) + Cl-
2NH3 + 3HOCl --> N2(g) + 3H+ + 3Cl- + 3H2O
H+ + OCl- --> HOCl

Note that the processes that consume the chlorine (breakdown from sunlight and oxidation of ammonia and nitrogenous organics) produce hydrogen ion (from HOCl or no pH change from OCl-) that exactly counteracts what was formed during the production of the chlorine. The net result of producing chlorine from a salt cell and then having it consumed is as follows:

2Cl- + 4H2O --> 2H2(g) + 2HOCl + 2OH-
2HOCl --> O2(g) + 2H+ + 2Cl-
----------------------------------------------
2H2O --> 2H2(g) + O2(g)

6Cl- + 12H2O --> 6H2(g) + 6HOCl + 6OH-
4NH3 + 6HOCl -->2N2(g) + 6H+ + 6Cl- + 6H2O
----------------------------------------------
4NH3 --> 6H2(g) + 2N2(g) -or equivalently- 2NH3 --> 3H2(g) + N2(g)

So you can see that the normal process of producing chlorine through an SWCG results in no net change in pH. Instead, Hydrogen and Oxygen gases are produced (when chlorine is broken down by sunlight) or Hydrogen and Nitrogen gases are produced (when chlorine is consumed by ammonia or nitrogenous organics) and I believe other organics can also produce carbon dioxide since the oxidation is similar to burning.

With liquid chlorine, the net result is somewhat similar except that the net result is the production of salt (sodium Na+ and chloride Cl-) along with oxygen gas from the breakdown of chlorine by sunlight or nitrogen gas when chlorine is consumed by ammonia and nitrogenous organics. So using liquid chlorine increases TDS (specifically salt) over time while an SWCG does not (the chloride ion consumed in production and turned into chlorine simply goes back into chloride ion during chlorine consumption).

Richard

PatL34
08-20-2006, 04:08 PM
Pat,

You do a very good job explaining the chemistry in simpler terms for people to understand. Thank you for doing that. There are a couple of corrections to what you wrote in your thread, but they don't detract from the main points too much except that it is not true that the production AND consumption are an alkaline (basic) process because they are not -- the net of the two (production and consumption) are neutral in pH.

The statement above corroborates what SWCG/liner pool owners have been saying in that they see very little change in pH over close to a week. I would have to say that what SWCG/plaster pool owners like me are seeing is a continuous leaching of Ca(OH)² from the plaster, and hence continuous addition of acid to neutralize this. This appears to clear up an anomaly about the steady pH in SWCG/liner pools. Thanks.

The products from electrolysis are only Hydrogen (H2) gas and Chlorine (Cl2) gas. There is no sodium (Na+) produced nor consumed by this process. There are also no hydroxide ions (OH-) directly produced from the process, but because hydrogen ions (H+) are consumed and due to the balance of the two with water, the net effect is as if hydroxide ions are created (from water).

2H+ + 2e- --> H2(g)
2Cl- --> Cl2(g) + 2e-
Cl2(g) + H2O --> HOCl + H+ + Cl-
H2O --> H+ + OH-
----------------------------------------
Cl- + 2H2O --> H2(g) + HOCl + OH-

Now compare the above with introducing liquid chlorine into the water:

NaOCl + H2O --> Na+ + HOCl + OH-

You can see that both process result in the same "HOCl + OH-" and therefore have the same slightly alkaline (basic) effect on pH. The effect is not strong because HOCl is a weak acid that partly counteracts the OH- (so some product is OCl- + H2O).

If we just stopped here, then one would conclude that both the SWCG process and adding liquid chlorine cause a rise in pH and though that is true, it is not the whole story. The chlorine doesn't just keep growing and growing in concentration in the pool. Instead, it gets used up. There are several processes that use up chlorine and I list some of these in this post (http://www.poolforum.com/pf2/showpost.php?p=27573&postcount=12), but the net result is that these processes do the following:

2HOCl --> O2(g) + 2H+ + 2Cl-
2OCl- --> O2(g) + Cl-
2NH3 + 3HOCl --> N2(g) + 3H+ + 3Cl- + 3H2O
H+ + OCl- --> HOCl

Note that the processes that consume the chlorine (breakdown from sunlight and oxidation of ammonia and nitrogenous organics) produce hydrogen ion (from HOCl or no pH change from OCl-) that exactly counteracts what was formed during the production of the chlorine. The net result of producing chlorine from a salt cell and then having it consumed is as follows:

2Cl- + 4H2O --> 2H2(g) + 2HOCl + 2OH-
2HOCl --> O2(g) + 2H+ + 2Cl-
----------------------------------------------
2H2O --> 2H2(g) + O2(g)

6Cl- + 12H2O --> 6H2(g) + 6HOCl + 6OH-
4NH3 + 6HOCl -->2N2(g) + 6H+ + 6Cl- + 6H2O
----------------------------------------------
4NH3 --> 6H2(g) + 2N2(g) -or equivalently- 2NH3 --> 3H2(g) + N2(g)

So you can see that the normal process of producing chlorine through an SWCG results in no net change in pH. Instead, Hydrogen and Oxygen gases are produced (when chlorine is broken down by sunlight) or Hydrogen and Nitrogen gases are produced (when chlorine is consumed by ammonia or nitrogenous organics) and I believe other organics can also produce carbon dioxide since the oxidation is similar to burning.

With liquid chlorine, the net result is somewhat similar except that the net result is the production of salt (sodium Na+ and chloride Cl-) along with oxygen gas from the breakdown of chlorine by sunlight or nitrogen gas when chlorine is consumed by ammonia and nitrogenous organics. So using liquid chlorine increases TDS (specifically salt) over time while an SWCG does not (the chloride ion consumed in production and turned into chlorine simply goes back into chloride ion during chlorine consumption).

Richard

I will revise my writeup accordingly to reflect what we discussed.

Pat

KurtV
08-20-2006, 06:04 PM
Pat,
Are you (and others) seeing constantly rising calcium hardness? I am not, yet I still have the huge acid demand.

chem geek
08-20-2006, 06:59 PM
Kurt makes a good point. We have not gotten to the bottom of this significant rise in pH some users experience, though we are making progress. As far as I can figure out so far, the following are possible sources of pH rise:

1) High TA and/or Low pH and/or high aeration. This refers to my CO2 outgassing chart (http://richardfalk.home.comcast.net/pool/CO2.htm) though this chart is very qualitative due to variance in aeration. This process has been proven through several users successfully eliminating their pH rise by lowering their alkalinity to 80 or even lower (or their pH to 7.2 in one case). This process can be distinguished from the others by the continual drop in TA over time (after adding acid to restore pH). NOTE: It's techically carbonate alkalinity that drives the CO2 outgassing, not TA, so adjustments should be made for CYA levels or Borates (Boric Acid; sodium tetraborate) that are used. My chart assumes no borates and 30 ppm CYA.

2) Curing of plaster (technically, the concrete in plaster/gunite). When enough Calcium Hydroxide has been produced from the curing process to raise the Calcium Hardness level by 10 ppm (which is probably the minimum detectable amount in test kits), this causes a rise (with a TA of 100) of 0.91 in pH so that 43 ounces of Muriatic Acid are needed (for a 16,000 gallon pool) to restore back to a 7.5 pH. So, the rise in CH will be relatively slow, though if you see it rise about 10 ppm after cumulatively adding 5-6 cups of acid over time (per 16,000 gallons), then this may be the cause of the pH rise. I also would expect that this curing process wouldn't last (in significant amounts) much more than 1 year at the most and that most of the curing would occur in the first 3-6 months. Don't forget that backwashing DE and sand filters as well as splash-out will dilute the CH (and everything else) over time so may hide the rise in CH (at a CH of 300, a loss of 10 is a 3.3% dilution or 333 gallons per 10,000 gallons in a pool). On the other hand, evaporation and refill will tend to increase CH unless the fill water has no CH.

3) SWCG systems that do not fully dissolve their generated chlorine gas. For every 1 ppm of chlorine that is generated and does not dissolve, this causes a 0.15 rise in pH which requires about 8 ounces (1 cup) of acid to restore pH (in a 16,000 gallon pool). My hunch is that after #2 above for newer plaster/gunite pools, that this is the main reason for rising pH in SWCG pools, but I have no proof of this (yet). One experiment to try is to use a lower power setting and run for a longer period of time (to make up for the lower power setting in terms of total chlorine produced in a day). In theory, the lower power setting should produce smaller bubbles and amounts of chlorine per volume of water flow and should have more chlorine dissolve in the water vs. outgassing to cause a rise in pH.

4) Other factors. These include fill water that is high in pH. Bather sweat is probably not very alkaline and rain is normally acidic so these are not likely to increase the pH.

Kurt's data showed that at least part of the pH rise was due to the outgassing of CO2 since his TA kept dropping. Kurt, if you are willing, continue to let it drop to about 50 (see this post (http://www.poolforum.com/pf2/showthread.php?t=4889&page=2) for an example of where that worked for someone else. That still provides some buffering, but would virtually slow to a crawl the CO2 outgassing (at a pH of 7.5 or above). Someone who has an SWCG system and experiences rising pH can also try the experiment I mention in #3 above to lower your power setting and increase your time on your SWCG. Let us know what happens if you do this! Oh yes, and Kurt, how old is your pool if it's plaster/gunite?

Kurt, if you do conclude that your specific source of rising pH is the outgassing of CO2, then you might consider adding 50 ppm Borates (sodium tetraborate) to act as a substitute buffer replacing part of your carbonate buffer system. That would let you run with much, much lower TA readings. Before we get to that point, however, we need to see if you can get to a low TA level where the pH rise slows down significantly.

Richard

PatL34
08-21-2006, 09:44 AM
Kurt,

As I am still curing my Diamond Brite plaster, my last CH reading was 270 ppm.

I filled the pool entirely with softened water, to help the curing, and tried as much as I could to keep the pH to between 7.2 - 7.6 using roughly a pint of acid a day.

During the first month I kept the SWCG off line, and used trichlor and bleach to maintain about 5 - 7 ppm Cl. Once I got to about 90 ppm CYA, I started using bleach only. I have not added any baking soda, letting the TA build up of its own accord.

As of now The PoolPilot SWCG is on at a power level of 1 and 50% output. So far no hint of algae, and I can only ascribe this to the plasterer who really knew what he was doing, and to what I am doing.;)

I will be taking a full set of figures today, and let you know what I have.

Pat

chem geek
08-21-2006, 02:20 PM
I have not added any baking soda, letting the TA build up of its own accord.
Normally the curing would produce Calcium Hydroxide and would not raise the TA. The TA would only rise if Calcium Carbonate was released into the pool. After curing, this would be considered "corrosion" of the pool surface. I'm not sure if it is normal for this to occur during the curing process. Did your pool contractor say that it was normal not only for CH to rise, but for TA to rise during curing or do you know if that's true from any other source?

It would be great, after we have this all figured out, to put together a simple flow chart that people can follow that would explain the normal processes they can expect in their pools. New plaster/gunite pool in first year -- rising CH (and TA?) and especially pH. TA > 80 and/or pH < 7.4 and/or lots of aeration -- rise in pH. Etc. Some would just be explanatory items while others could have solutions.

Richard

PatL34
08-21-2006, 02:58 PM
Richard,

I should have added baking soda to bring the TA up to 100 ppm, so you are correct again. Bear in mind that this information came from most of their customers, presumably plasterers. (See the Diamond Brite installation manual in the PDF below.)

I do know that the CH will rise when curing, as this was my experience the first time i used Diamond Brite, but am not sure about the TA going up. I do think that by keeping the Ca(CO3)² and pH down it would help more in the curing process. Just a theory of mine.

I agree that a flow chart would be nice, but feel many poolowners are more interested in swimming, rather than the mechanics of plaster curing. So it would be available to the dedicated few like ourselves, but can we tell new pool owners having plaster pools under construction what the experiences we have been having.

Pat

http://sgm.cc/download/installationmanual-DiamondBrite.pdf

KurtV
08-21-2006, 03:33 PM
...

2) Curing of plaster (technically, the concrete in plaster/gunite). When enough Calcium Hydroxide has been produced from the curing process to raise the Calcium Hardness level by 10 ppm (which is probably the minimum detectable amount in test kits), this causes a rise (with a TA of 100) of 0.91 in pH so that 43 ounces of Muriatic Acid are needed to restore back to a 7.5 pH. So, the rise in CH will be relatively slow, though if you see it rise about 10 ppm after cumulatively adding 5-6 cups of acid over time, then this may be the cause of the pH rise. I also would expect that this curing process wouldn't last (in significant amounts) much more than 1 year at the most and that most of the curing would occur in the first 3-6 months. Don't forget that backwashing DE and sand filters as well as splash-out will dilute the CH (and everything else) over time so may hide the rise in CH (at a CH of 300, a loss of 10 is a 3.3% dilution or 333 gallons per 10,000 gallons in a pool). On the other hand, evaporation and refill will tend to increase CH unless the fill water has no CH.

This is why I asked Pat whether he was continuing to see calcium hardness increase. I have not see any increase at all in the 8 or 9 months I've had my Diamond Brite finish installed. None. In fact, because my fill water has a CH of 50 ppm, I occasionally have to add calcium to replace that lost to splash out and backwashing. This can't be the source of my pH rise.

...

4) Other factors. These include fill water that is high in pH. Bather sweat is probably not very alkaline and rain is normally acidic so these are not likely to increase the pH.
My fill water has a pH of about 8.0 but as I add little of that I probably isn't a significant contributor.

Kurt's data showed that at least part of the pH rise was due to the outgassing of CO2 since his TA kept dropping. Kurt, if you are willing, continue to let it drop to about 50 (see this post (http://www.poolforum.com/pf2/showthread.php?t=4889&page=2) for an example of where that worked for someone else. That still provides some buffering, but would virtually slow to a crawl the CO2 outgassing (at a pH of 7.5 or above). Someone who has an SWCG system and experiences rising pH can also try the experiment I mention in #3 above to lower your power setting and increase your time on your SWCG. Let us know what happens if you do this! Oh yes, and Kurt, how old is your pool if it's plaster/gunite?
I suspect you're right about a significant portion of my pH rise coming from CO2 outgassing. I've been letting the alkalinity drop for several weeks after reading your other posts on the subject but haven't seen any benefit from it so far. I'll let it continue down to 50 ppm; I'll probably be there within a week.

Kurt, if you do conclude that your specific source of rising pH is the outgassing of CO2, then you might consider adding 50 ppm Borates (sodium tetraborate) to act as a substitute buffer replacing part of your carbonate buffer system. That would let you run with much, much lower TA readings. Before we get to that point, however, we need to see if you can get to a low TA level where the pH rise slows down significantly.
I've considered this also since reading Evan's posts on the subject. I'll probably wait until later this fall when the pool is unswimmably cool to start messing around with that.

Richard

I'll update my data this evening. I might actually be starting to see a bit of slackening in the rate of pH rise.

Is there starting to be some consensus here that SWGs themselves have gotten an undseserved reputation as the source for constant pH rise even if we can figure out what the real culprit is?

Pat,
You might be interested to know that I finally took the SWG plunge. I'm hoping my AquaRite will arrive in the next couple of days.

PatL34
08-21-2006, 04:27 PM
I'll update my data this evening. I might actually be starting to see a bit of slackening in the rate of pH rise.

Is there starting to be some consensus here that SWGs themselves have gotten an undseserved reputation as the source for constant pH rise even if we can figure out what the real culprit is?

I figure that those with plaster pools will always see a rise in pH with or without a SWCG. It will probably occur with vinyl pools, but so slowly, it will be hard to distinguish. It is looking more like the nature of the beast, or as one of my teachers said way way back, an "inherent feature of the system". I hope Richard will come up with an answer that breaks that hypothesis.;)

Pat,
You might be interested to know that I finally took the SWG plunge. I'm hoping my AquaRite will arrive in the next couple of days.
Way to go Kurt.:D

You are going to love every minute it is running. Guaranteed!!:cool:

Pat

dawndenise
08-21-2006, 06:16 PM
Just wondering. Do you have any water features (waterfalls, etc.) or would you say that your pool doesn't have much aeration? What brand of SWG system are you using? Do you use a pool cover and is it opaque or a clear "solar" cover?

Since you aren't seeing the same sort of pH rise that others see in SWG pools, I'm just trying to figure out what's different about your pool.

Richard

I have a waterfall that's on 12 hours a day, so lots of aeration! I have an Aquarite SWG. No pool cover of any kind, lots and lots of UV on the pool - we're on Day 52 of air temps at 100 degrees or higher.

Also, although I WAS just on my 3rd gallon of muriatic, I've now broken the seal on the 4th gallon.

KurtV
08-21-2006, 10:23 PM
Richard,
Updated data. I think the acid demad might be letting up a bit.

Date pH Alk. Acid addition
7/26 7.8 100 24 oz.
7/27 7.4 100
7/28 7.8 100 16 oz.
7/29 7.7 100 16 oz.
7/30 7.2 90 32 oz. (before testing)
7/31 Vacation
8/1 Vacation 16 oz.
8/2 Vacation
8/3 Vacation 16 oz.
8/4 7.8 90 28 oz.
8/5 7.6 80 16 oz.
8/6 7.6 80 16 oz.
8/7 7.4 80 8 oz.
8/8 7.6 70 16 oz.
8/9 7.6 70 16 oz.
8/10 7.5 70 16 oz.
8/11 7.3 70 8 oz.
8/12 7.4 70 16 oz.
8/13 7.6 70 16 oz.
8/14 Work trip
8/15 7.6 70 16 oz.
8/16 7.6 70 24 oz.
8/17 7.4 file:///C:/DOCUME%7E1/CLV/LOCALS%7E1/Temp/moz-screenshot-2.jpgfile:///C:/DOCUME%7E1/CLV/LOCALS%7E1/Temp/moz-screenshot-3.jpg65 16 oz.
8/18 7.4 60 8 oz.
9/19 7.5 60 20 oz.
8/20 7.2 60 8 oz.
8/21 7.4 60 8 oz.

chem geek
08-22-2006, 12:47 AM
Kurt,

I'll bet that when you hit 50, if you let the pH rise to 7.5 then the continued rise from there will be slow (i.e. you could add acid when it hits 7.6 or 7.7). You could therefore make your pH "target range" 7.5-7.7 and not use too much acid. In fact, the general advice for people with low TA would be to have higher pH for better water balance though this technically is only necessary for grout/plaster/gunite pools. Anyway, thank you so much for keeping such good track of your numbers. It really helps in trying to figure these things out.

By the way, if the TA is somewhat stuck on 60 and getting lowered too slowly, you can always just add some extra acid to get to a pH of 7.2 or below in order to accelerate the outgassing (i.e. Ben's alkalinity lowering technique), but if you have the time and just want to see how things slow down as TA gets lower, then measure on...

Richard

Davenj
08-22-2006, 07:33 AM
Great read and interesting research. I was surprized on the acid demand of a gunite pool. I have a vinyl pool, 16oz a week. Didn't mean to muck up your thread. Keep up the work, look forward to future posts.

South_Texas_Sun
08-22-2006, 08:54 AM
We just finished (sort of) our 19,000 gallon IG pool here in south central Texas and I've been wondering why I've had to add acid about every 2 or 3 days....lol

We have 4 waterfalls, of which just the spa spillway waterfall runs 8 hours/day, but it's a healthy stream of water, dropping about 5 feet though the air, and there's 2 Jandy Sheer Descents and a 12 foot rock slab "grotto" waterfall.

As part of the pool equipment, we got a cheapo "test kit" for chlorine and PH ONLY, but I ordered the poolforum test kit (with salt option) about 3 or 4 weeks ago, and haven't received ANYTHING......not even an EMAIL when threatening to cancel the order! (so I can't verify any numbers except that my Hayward SWG is working and the PH is rising like crazy.)

Another variable.....we have underwater limestone flagstone on 2 separate larg-ish entry and spillway beaches (each 8'X5'). Would underwater limestone rock increase the alkalinity? (it doesn't seem to be reacting to the salt water, but there is substantial initial flaking which is normal, according to all reports) Would it help to place a less alkaline stone below the spa spillway?

Can anyone recommend a more readily available test kit that I can buy online, so that I can get some numbers on my pool chemistry?

Very interesting topic. Thanks for all the great discussion! :)

STS

PatL34
08-22-2006, 09:06 AM
STS,

I suspect that the limestone will have some effect vis-a-vis your rising pH. Chem_Geek hopefully will chip in here. The muriatic acid will do some work on the limestone, so some adjustments will have to be made.

If you can get access to a Taylor 2006 test kit, it will be a great help in testing your water while waiting for Ben's PS234 kit. The numbers will then help us to help you.

Kurt, the numbers I took this morning were:
FC 5 ppm
pH 7.2
TA 90 ppm
CH 270+ ppm (ran out of R-0012 reagent. Duh!)
CYA 60 ppm

Will get another CH reading later today.

Pat

chem geek
08-22-2006, 01:23 PM
Limestone is primarily calcite which is calcium carbonate, the same major component that is used in the production of cement that is in plaster/gunite/grout so the same rules for water balance apply. I don't believe the issue of corrosion vs. scaling will be any different for limestone than for the plaster/gunite/grout except perhaps that the limestone may be more sensitive to this chemical balance since it is much more "pure" calcium carbonate (i.e. doesn't have its calcium carbonate converted to calcium oxide bound to silicon oxide in cement though the aggregate in concrete is often limestone).

So I wouldn't expect a change in pH from the limestone unless your water was out of balance. If your water was too low in TA, pH and/or CH, then you could corrode the calcium carbonate from the limestone and that would slightly increase your CH and TA and would increase your pH.

Richard

bbb
08-22-2006, 05:35 PM
Very interesting thread. This is my first year with a SWG (installed in June '06), and I live in the Northeast. The pool is a vinyl liner, 20x40, around 20 years old. CYA around 45. No special features. Over the past 2 years the only thing I have used to raise pH is borax. My pH has been between 7.2 and 7.4 all summer. Total acid added - zero! Contributing factors may include lots of acid rain, and my use of a solar cover when the pool is not in use. I have added virtually no fill water all year.

nater
08-29-2006, 12:45 PM
Great thread!!

My experience closely matched bbb's with regards to stable pH in a vinyl pool with a SWC. At least until I added a....drumroll....FOUNTAIN!!!! :)

The fountain was added back in early June to combat rising pool temps. It's done a great job of that. Last year by this time my water temp was in the mid 90's, this year I've kept it between 82 and 86.

I added my SWC in ealry March, before the swim season started. I then found this site (thank God) and balanced my water within a week or two. I've reduced my CYA down from 120+ to a current level of 50-60. Prior to June, I had added nothing but salt when needed.

Since installing the fountain I've been using about 1 gallon of MA and 4# of Baking Soda every 2 weeks to maintain a pH of roughly 7.5 and Alk around 120-140. Why? To keep my pool "on target".

Since reading the latest posts on lowering ALK to keep pH rise under control, I'm fully ready to let things go for a couple weeks and see where they settle out naturally.

Chem Geek/others, any suggestions to make my experiment more controlled and useful to the larger group?

Current numbers as of last night (I had to drain about 7,000 gallons Sunday to repair a crack in my steps and rebalanced after the re-fill).

Temp: 82
FC: 3.5
TC: 3.5
pH: 7.2
Alk: 140
CH: 100
CYA: 55
Salinity: 3300
Borates: 50-60 ppm (strips)
Phosphates: less than 1000 ppb (Hach test)

chem geek
08-29-2006, 01:30 PM
nater,

Thank you for your very detailed set of numbers. Now that I have borates added to my spreadsheet, I can give you an idea of where I think you are at and where you can go from here.

Your CO2 outgassing rate number (at pH 7.2) is 27.8 which is very, very high so it's no wonder you are having to add so much acid and baking soda to your pool (at a pH of 7.5 it's a much more reasonable 12.8 which would probably be stable were it not for the fountain -- which is exactly what you have been seeing). In general, whenever you are not only adding acid, but also have to add baking soda to maintain TA, then you are seriously outgassing CO2 and should consider lowering TA and/or raising pH (unless you like spending money and time on acid and baking soda!). Even before the fountain, I would say you were somewhat lucky in not having to add so much acid and baking soda, but now with the fountain adding to the aeration, you can really see how "overly carbonated" your pool is.

If I assume you are at a baseline pH of 7.5 most of the time, then your acid and baking soda additions mean that you outgas 11.5% of your carbonate in your pool every 2 weeks and you have an additional source of base (pH rise) in your system since your additions would normally lower the pH to 7.36 and the TA to 130.6 over a 2 week period. It is as if you have an additional source of rising pH equivalent to 20.5 ounces of lye (sodium hydroxide) so perhaps this is from your chlorine generator. In fact, if your SWCG were to produce 5 ppm of chlorine over the 2 weeks that got outgassed as chlorine gas (i.e. didn't dissolve into the water to produce hypochlorite), then that would be consistent with the numbers that you gave.

So here's a plan that can be done in two steps to isolate the two sources of rising pH that you have -- CO2 outgassing and SWCG chlorine outgassing (assuming that's what's going on). First, follow Ben's Lowering Your Alkalinity Procedure (http://www.poolforum.com/pf2/showthread.php?t=191) to get your TA down to 80. Then we can see what happens. My guess is that you will still need to add acid (though less of it -- probably a little more than 6 cups every 2 weeks), but that you may not need to add baking soda anymore. I assume you will try to keep your pH at 7.5 (not 7.2).

Assuming the lower TA works for you (and you may need to get it lower than 80, but let's see where you are at there first), then you can see if you can lower the power level of your SWCG and have it run for a longer period of time (to make up for the lower power level) to see if this helps reduce the amount of wasted generated chlorine that may be escaping as chlorine gas and not getting dissolved into your pool as hypochlorite. If this works, then this will further lower how much acid you need to add to your pool.

Sound like a plan?

Richard

nater
08-29-2006, 08:15 PM
Sounds like a plan.

Just tested again, and pH is up 0.1 to 7.3, and Alk has dropped 20ish to 110 with only the jets "rippling" the surface. I'll turn on the fountain tonight, keep the SWC at 30% OP and track CL, ALK, and pH with temp over the next several days while not adding anything to the pool (barring any unpleasant surprises from Ernesto).

Question: With TA around 80, what's my lower limit on pH to limit any potential corrosion to my light ring or SWC cell?

Thanks.

chem geek
08-29-2006, 09:09 PM
Since you have a vinyl pool, you can't have corrosion in the "calcium carbonate" sense which is why you don't have your CH up at 300 or so as you would in a plaster/gunite pool. Corrosion of metal surfaces (especially stainless steel, galvanized metal, and copper) is unlikely to occur if you keep your pH above 7.0 at all times and I would just shoot for around 7.4-7.6 which is generally better on the eyes anyway. The purpose of TA in your vinyl pool isn't so much to prevent corrosion as it is to act as a pH buffer, but you don't need much of it to get this buffering effect and as you've found out, too much is not good either as it causes more CO2 outgassing (and pH rise).

Richard

KurtV
08-29-2006, 11:18 PM
Another update on my situation: Alkalinty is now at 50 ppm and pH has gone from 7.3 to 7.4 over the last 4 days without adding any muriatic acid; a vast improvement. We'll see how it goes from here but I'm very hopeful that my acid comsumption is going to go way down.

As to my original theory, from all the stories I've read here and elsewhere, I'm becoming covinced that it's at least somewhat valid; SWGs themselves are not the underlying cause of rising pH.

chem geek
08-30-2006, 12:52 AM
Kurt's post just had me get the idea that perhaps the hydrogen gas generation in the salt cell which has hydrogen gas bubbles coming out of the return jets may act like "aeration" and accelerate the outgassing of carbon dioxide. You know how dropping sugar crystals or other substances into carbonated beverages (including champagne) has lots of bubbles coming from these "nucleation sites"? Well, perhaps hydrogen gas bubbles act somewhat like nucleation sites for the dissolved carbon dioxide -- or they act as mini-atmospheres just as bubbling air might do in the pool water.

In fact, given how incredibly productive the TA lowering procedure is when one uses "tiny bubbles" from an air compressor, I really think that the hydrogen gas from the SWCG systems may simply be accelerating the carbon dioxide outgassing process (sorry for repeating myself, but I'm really excited about this, thus proving once and for all that I am a true nerd).

Richard

KurtV
08-30-2006, 07:36 AM
Richard,
Sounds plausible, but why doesn't everyone with an SWG see the constant upward presure on pH?

nater
08-30-2006, 08:03 AM
Has anyone discussed how a solar cover comes into play? The other change in my pool besides adding the fountain was NOT using the solar cover due to the hotter weather. With the cover on, there's a very limited surface area for the CO2 exchange. We should add cover usage to the variable list.

chem geek
08-30-2006, 08:39 PM
Richard,
Sounds plausible, but why doesn't everyone with an SWG see the constant upward presure on pH?
Possibly due to lower TA and higher pH that some people have. Maybe some SWG's produce different sized bubbles -- larger bubbles would be less efficient than smaller bubbles as was borne out by the "nozzle" experiment to lower TA.

We should add cover usage to the variable list.
Yes, using a cover significantly reduces CO2 outgassing. Or course, with an SWCG system, are people told never to use a cover or to only cover part of their pool? Otherwise they could build up a large bubble of hydrogen gas under their cover. It's not "explosive" the way propane would be, but it certainly burns (if ignited by flame or a spark) when mixed with oxygen (remember the Hindenburg!).

Richard

Sentient
08-31-2006, 01:38 AM
Possibly due to lower TA and higher pH that some people have. Maybe some SWG's produce different sized bubbles -- larger bubbles would be less efficient than smaller bubbles as was borne out by the "nozzle" experiment to lower TA.
I missed that, what was the nozzle experiment?


Yes, using a cover significantly reduces CO2 outgassing. Or course, with an SWCG system, are people told never to use a cover or to only cover part of their pool? Otherwise they could build up a large bubble of hydrogen gas under their cover. It's not "explosive" the way propane would be, but it certainly burns (if ignited by flame or a spark) when mixed with oxygen (remember the Hindenburg!).
I have a cover and run the generator with it covered often. If it builds up a bubble, I don't see it. I suspect the cover is porous to hydrogen and it isn't getting a chance to build up. Your speculation does suggest an experiment though. Holding a lighter or match above the bubble stream of my primary return should produce some combustion if hydrogen is being produced. It would not be visible to the eye, but should show up on a digital camera or digital video camera. Those image sensors are quite sensitive to IR. Would chlorine burn too? Would there be a characterisitc color?

This is a don't try this at home, mythbuster kind of experiment. I suspect there is potential for real danger, small potential, but real.

Actually I am more tempted to look on the underside of the cover for discoloration. Since I see significant pH rises, if it is due to chlorine gas in the bubble stream going into my pool when the SWG is on, then there should be fading or hardening of the material above the first return jet where most of the bubbles enter the pool. Perhaps I can check those ideas out over the weekend.

chem geek
08-31-2006, 07:28 PM
I missed that, what was the nozzle experiment?

Holding a lighter or match above the bubble stream of my primary return should produce some combustion if hydrogen is being produced. It would not be visible to the eye, but should show up on a digital camera or digital video camera. Those image sensors are quite sensitive to IR. Would chlorine burn too? Would there be a characterisitc color?

Actually I am more tempted to look on the underside of the cover for discoloration. Since I see significant pH rises, if it is due to chlorine gas in the bubble stream going into my pool when the SWG is on, then there should be fading or hardening of the material above the first return jet where most of the bubbles enter the pool. Perhaps I can check those ideas out over the weekend.
Look at this thread (http://www.poolforum.com/pf2/showthread.php?t=4492&highlight=nozzle) for more info on the use of compressors, on nozzle size and bubble size, and other info related to aeration.

If you do the flame experiment with the pool uncovered, then you aren't going to do anything dangerous since the amount (rate) of hydrogen produced isn't particularly large. In fact, I used to do some water experiments at home producing oxygen/hydrogen (using carbon cores from batteries for the "plates") and also could smell some chlorine from it as well, especially when I added lots of salt. When I lit the hydrogen bubbles, you would just get some minor popping. I didn't notice any color.

Chlorine is not flammable or combustible (it's an oxidizer just like oxygen it can't "burn") though it can be combustible (generate lots of heat) when combined with other compounds such as ammonia.

I don't know what chlorine gas does to covers. It is certainly a corrosive oxidant, but I just don't know what, if anything, it would do to a solar cover. Let us know your results of all your experiments and observations, and please be careful in any event -- the use of gloves and goggles would be wise to be extra safe.

Richard

Sentient
09-06-2006, 08:23 PM
Look at this thread (http://www.poolforum.com/pf2/showthread.php?t=4492&highlight=nozzle) for more info on the use of compressors, on nozzle size and bubble size, and other info related to aeration.
.
.
.
I don't know what chlorine gas does to covers. It is certainly a corrosive oxidant, but I just don't know what, if anything, it would do to a solar cover. Let us know your results of all your experiments and observations, and please be careful in any event -- the use of gloves and goggles would be wise to be extra safe.

Thanks for the link to the aeration post. I am trying to get my alkalinity down as others are. I want to see if it reduces my acid usage a bit.

I swam under the cover and see no discoloration at all. So either my bubbles are pretty much all hydrogen, or the cover is immune to the chlorine, at least in a visible way. So I would call that a non-result with no real information gained. I didn't have time to play with fire this weekend, perhaps tonight.

Mark

klharmon
09-18-2006, 11:04 PM
I go through about 1/2 gallon a week of muriatic acid on my 19,000 gal in ground pool, and I have an AquaPure 1400 SWG. I have a waterfall feature that I use rarely, so a majority of the time the pool just vacs & filters.

pool is relatively new, plaster bottom, and I check pH twice a week.