Algae, TA or what?

[PoolDoc]

Hi All;

Richard, I've finally taken the time to look at your Pool Calculations spreadsheet. Very impressive! I started something similar, years ago, but got nowhere near as far as you have. I'm asking Madison (my older son, who's close to finishing his degree in biology) to start working through your spread sheet today.

[ A couple of questions:
1. Have you done the calculations for peroxide / chlorine interactions (dechlorination) and the interaction between monopersulfate and chlorine?
2. It may be there, but do you have the calculation for the carbonate fraction of the TA, given a specific value for TA, CYA, & borates? Do you have an 'adjusted' SI, based on the presumptive carbonate ppm?
3. Do you have a version with references to equation sources, etc.? ]

Carl, Richard's calculations and analysis of the relations between pH change, TA, off gassing and so on are plausible. I can't verify them yet, but they do fit my own field experience, so that's confirmatory.

My inclination, at this point, is to accept them -- and their implication that low TA is to be desired, generally -- for NON-concrete pools.

I want to understand them better, and consider what the implications are on CONCRETE pools (and what Richard has to say) before jumping on them for concrete pools. There is some risk there, that a wrong judgment would lead to pool damage. However, that whole area of "what's happening to the plaster" is a realm of much more heat than light. Just about all the research done in that area has been paid for or done by folks with a really big axe to grind.

I do think we need to be observant, and see if field reports from PF users confirm or dis-confirm the idea that lower TA (and particularly, lower carbonate alkalinity) leads to greater pH stability.

I'm going to email you all (mods + Richard) a 'modest proposal'. I'll try to get it out today, but it may be tomorrow. Richard has done a LOT of work with gathering together the chemistry relevant to pools. Years ago, I found myself puzzled by the fact that, although most of the chemistry Richard is working with is not new (open to correction here) no one seemed to have put it "all together". Richard appears to have gone a very long way toward that.

But, it's going to be hard (at least for me) to digest all that he's done, in order to get clear in my mind what to tell people.

I do have one question to you all (that is, anyone who bothers to read this section, but particularly the mods and Richard):

How interested are you all in changing pool chemistry -- not just for the 100,000 or so who follow PF and TFP closely -- but for the majority of pool users?

I think I see a path to doing so, but it would require more than just Richard, and more than just me, working toward that end. It would be a worthwhile thing to do, I think.

But it would (in the end) seriously affect BioLab as it exists today. And they drive the NSPF, many commercial pool codes, and the shape of "ideal" pool chemistry.

(As you respond, keep in mind that BioLab probably will read this. When I last checked, several years ago, connections from their corporate network were ALL OVER this site and PoolSolutions.)

Ben Powell

[CarlD]

Carl, Richard's calculations and analysis of the relations between pH change, TA, off gassing and so on are plausible. I can't verify them yet, but they do fit my own field experience, so that's confirmatory.

My inclination, at this point, is to accept them -- and their implication that low TA is to be desired, generally -- for NON-concrete pools.

...

I do think we need to be observant, and see if field reports from PF users confirm or dis-confirm the idea that lower TA (and particularly, lower carbonate alkalinity) leads to greater pH stability.

...

But, it's going to be hard (at least for me) to digest all that he's done, in order to get clear in my mind what to tell people.

I do have one question to you all (that is, anyone who bothers to read this section, but particularly the mods and Richard):

How interested are you all in changing pool chemistry -- not just for the 100,000 or so who follow PF and TFP closely -- but for the majority of pool users?

...

But it would (in the end) seriously affect BioLab as it exists today. And they drive the NSPF, many commercial pool codes, and the shape of "ideal" pool chemistry.

(As you respond, keep in mind that BioLab probably will read this. When I last checked, several years ago, connections from their corporate network were ALL OVER this site and PoolSolutions.)

Ben Powell

I'm a big believer in doing what actually works, not what I'd like to think works, what everyone says works, or even the mantras I've followed for 9 or 10 years now.

First off, let's divide "the world" into vinyl versus concrete/plaster pools as you suggest and keep this discussion solely to the vinyl (and I presume fiberglass) side. As you point out, the concrete/plaster side has all kinds of issues that may well require different standards than the vinyl side.

So, only for vinyl pool owners I'd like to see us start collecting empirical evidence that Richard's and Evan's low TA theory ("theory" in the scientific sense, not the popular sense) is valid. It will probably take a few seasons but, frankly, even if it were shown to not be valid, I don't see it doing much harm to people's pools or swimming experiences. In other words, it's a safe test for us to run.

In fact, I'll start lowering TA on my pool either tonight or this weekend--it's about 80, so getting it down to 50 should be a snap. Plus I've got my "splashers" to aerate it!

As for the pool chem companies, we are already NOT where they want to be. Even with our current recommendations of TA of 80-125, we tell people that baking soda is chemically the same stuff as "Total Alkalinity Raiser" and that washing soda is chemically the same stuff as "pH Up!" (which also raises T/A). We further tell people to use muriatic acid to lower TA (by lowering pH).

So we already advocate a T/A control system that does not require special chemicals only available from pool companies. If we simply move to advocating low T/A levels it doesn't affect them in any way that I can see.

Our recommendations with regards to when to use chemicals only they can make readily and publicly available: CYA, Calcium, Polyquat 60%, Tri-Chlor, Di-chlor, Cal-Hypo and Sequestering agents, remains unchanged.

So does our recommendations for chemicals to be avoided.

Again, my own limited experience is that I've ONLY ever had a drastic change in pH, or even a constant change in pH where there was a clear, explanable cause, such as the time I came home after 2 weeks and found my CYA at 60 and my pH below 6.8. I had put 4 floaters full of Tri-Chlor tabs in my pool. The good news was I had no algae.....At the time I was not yet aware that Tri-Chlor was heavily acid--that must have been 2003.

So, I guess what I would like to see is a set of TA levels recommended, somewhat similar to the table Richard has attached above, but, obviously with clearer guidelines (Not going for TA=40 and pH=8.0 to get perfect balance! )

Carl

[chem geek]

In fact, I'll start lowering TA on my pool either tonight or this weekend--it's about 80, so getting it down to 50 should be a snap. Plus I've got my "splashers" to aerate it!

Carl,

Unless your pool experiences a regular rise in pH over time, then lowering the TA isn't going to show any noticeable difference. Also, there is a slow upward pressure on pH from chlorinating liquid and bleach due to the "excess lye" and this varies by brand with 6% Clorox Regular unscented having the lowest with a pH of 11.9. Some off-brand bleaches have a pH of 12.5 or higher. Chlorinating liquid also varies with better 12.5% brands having a pH of 12.5 while others have 13 or higher. If you tell me the concentration and pH of your chlorine product and how much FC you use per day on average, I can tell you the pH rise (with TA assumptions) and amount of acid you need to compensate. No matter how low you lower the TA, you won't get rid of the need to compensate for this "excess lye".

As for recommended TA levels, when using a hypochlorite source of chlorine you generally don't want to go above 80 ppm, but with covered pools a higher TA isn't going to be much of a problem. As for how low to go, that depends on how much aeration there is in the pool and isn't easily calculated. So one would just have a more generic rule for those pools experiencing a regular rise in pH of letting the TA drop as low as 50 ppm if needed and seeing if this improves the rate of pH rise and then compensate pH and/or CH. For most pools, 70-80 ppm will be OK. It's SWG pools and pools with water aeration features that have more of an issue, partly due to increased aeration from hydrogen gas bubbles (though calculations show this probably isn't the entire effect) but also, I believe, from undissolved chlorine gas outgassing. This latter effect can't be compensated by TA and is probably worse in pools with short pipe runs from the SWG to the pool.

As for the point one needs to get in the carbon dioxide equilibrium chart before pH becomes stable, that is only able to be determined empirically and will be different for every pool since the rate of outgassing depends on the amount of air-water surface interaction so on aeration, wind, etc. Very roughly speaking, nearly everyone (with no pool cover) experiences a problem when they get into the red region with 20 or more times as much carbon dioxide in the water than the equilibrium amount from air, many have a problem in the orange region between 10 and 20, and most seem to do OK with some pH rise that is tolerable in the green region less than 10, but there are definitely those highly aerated pools who see a rise in pH until they get down to nearly 2 in the chart. For spas, the hotter temperature and vastly increased aeration from spa jets almost always has to get below 4 and sometimes down to 2 or 1 before the pH becomes stable. The use of 50 ppm Borates provides additional pH buffering when the TA is low, but without the negative pH rising side effect of the carbonate buffer system.

Thanks,
Richard

[CarlD]

"Covered"?

I use my solar cover (though not the last few days as the heat has been extreme) but do leave it off. It doesn't seal, of course.

Current TA is 80 so I guess I'll leave it there. pH hasn't moved from 7.6 all summer (it's usually 7.5 in past years). TA doesn't usually move much on me either. CYA is just under 50, FC is around 5. CH is pretty low--I don't measure it more than once or twice a season. I THINK it was 110 or 120. I have no real source of cal since I haven't used Cal-Hypo in a few years.

I generally use a higher qual LC that claims 12.5% but always tests at 14% (never thought to test the pH).

Normally, I add about half a gallon every other day, but lately, with the heat, I've been using more. In fact, this season, like almost everyone, I've used far more chlorine than usual. I've just drained the first gallon off my 5th carboy of the summer, and it's only early July. 5 is normally a full summer's worth.

I realize you are not "there" yet, but we are going to need practical guidance regarding TA levels "If you pH is this, and your FC is this, and...., and ...., then do THIS."

Thanks for all your hard work.

Carl

[sturev]

Hi Guys,

I'm willing to help if you want it. I have a unique pool that may help prove/disprove theories???

My pool is fully insulated and covered, it stays at a constant 88 degrees and is subjected to maybe an hour or so of sunlight a month (exercise in the evenings & the sun is off the pool). I have no CYA added to the water. I would think it would be considered a heavily aerated pool, as the counter current alone creates a lot of air bubbles and then put me in there flailing around trying to swim upstream ; the whole pool is filled with air bubbles for about 30-40 mins a day.

I've only used the BBB method on a fresh fill about 2 months ago. I have added a total of one box of Borax, 1/2 gal of Acid and 1.5 gal of bleach since the refill. I run FC between 2 & 4; only have to add 6 oz every 4 or 5 days. Right now my TA is on the high side (150; was 230 on fill and I've been working it down in the last few weeks). PH is 7.8, until I add acid to bring down the TA; it takes 48 hrs to go from 7.0 to 7.8.

Let me know if I can be of any help...

[Furbabyvet]

FWIW, I'm keeping the solar cover on the pool now and the pH seems to be rising more slowly, not to mention the chlorine disappearing more slowly. I just wish it didn't make it feel like you're swimming in a nice, comforting bowl of tomato soup . Gotta get a solid color cover...

[PoolDoc]

@ Sturev: thanks for the offer. I'll try to keep that in mind -- I'm working on some plans, now for research, writing, and PoolForum development.

@ Furbyvet: thanks for the info. Your response represents a confirmation of Chem Geek's analysis of TA and pH rise in pools.

Ben

[chem geek]

[ A couple of questions:
1. Have you done the calculations for peroxide / chlorine interactions (dechlorination) and the interaction between monopersulfate and chlorine?
2. It may be there, but do you have the calculation for the carbonate fraction of the TA, given a specific value for TA, CYA, & borates? Do you have an 'adjusted' SI, based on the presumptive carbonate ppm?
3. Do you have a version with references to equation sources, etc.? ]
:
I want to understand them better, and consider what the implications are on CONCRETE pools (and what Richard has to say) before jumping on them for concrete pools.
:
Years ago, I found myself puzzled by the fact that, although most of the chemistry Richard is working with is not new (open to correction here) no one seemed to have put it "all together". Richard appears to have gone a very long way toward that.

1. I don't have hydrogen peroxide in the spreadsheet, but I've done the calculations for using it as a dechlorinator since people have asked about that. Roughly speaking, it takes the same volume of 3% hydrogen peroxide to neutralize a volume of 6% bleach (detailed calculations are in this post). As for monopersulfate, I do have the equivalent of that in the spreadsheet at line 359 "[HSO5-] assumed to be equal to [HSO4-]" which is a field that gets calculated when you enter in a quantity into the "NON-CHLORINE SHOCK" section. You can then adjust FC so that line 293 "Free Chlorine" matches in amount to 359 and that will give you the chlorine equivalent for the MPS. A pain, yes, but this question doesn't come up very much. Roughly speaking 3-1/2 teaspoons of Dichlor is equivalent to 5 fluid ounces of 6% bleach is equivalent to 7 teaspoons of non-chlorine shock (43% MPS) and is 7 ppm FC in 350 gallons and is the amount of oxidizer needed for every person-hour of soaking in a hot (104ºF) tub.

2. Yes, the Carbonate Alkalinity is in the first section on line 16. The S.I. calculations all use this adjusted TA (i.e. the carbonate alkalinity). I do not have any raw unadjusted S.I. using TA alone (that is, ignoring CYA and Borates). Note that my S.I. calculation comes from direct calculation of calcium and carbonate ion concentrations relative to the solubility product of calcium carbonate. I also derive the LSI formula in lines 436 through 481 which shows that it comes directly from the equilibrium of calcium and carbonate ions with calcium carbonate and has nothing to do with boiler systems, open vs. closed, etc.

3. I don't have a references chart, but I list a few in the spreadsheet. The constants for the chlorinated isocyanurates and for CYA come from the 1974 O'Brien paper. The most flaky, yet critically important, constant in the spreadsheet is for the solubility product of calcium carbonate where I ended up using consistent data from the CRC Handbook that resulted in closely matching the Taylor watergram. I also have constants from Wojtowicz that are used when you set 223, 224 and 225 (last three lines in that block) to TRUE in columns B and C. The ANSI/APSP-11 settled on S.I. tables that are a little closer to Wojtowicz are are generally 0.1 higher than my calculation (Wojtowicz is generally 0.15 higher than my calculation). The ion pair dissociation constants come from formation or stability constants mostly in a spreadsheet source I saved but would have to look up where that came from -- they aren't critical and only affect the saturation index by about 0.02 (unless sulfates are very high).

Using a lower TA in a concrete ("pool plaster") pool is fine so long as you compensate other parameters such as pH and/or Calcium Hardness (CH) to get the saturation index to near zero. This will saturate the water with calcium carbonate to protect such surfaces. Basically, the lower TA lowers carbonate ion but a higher pH does the opposite while CH increases calcium. Theoretically, a low TA and high CH combination is better in terms of calcium oxide since calcium carbonate saturation implies a constant right-hand side product while lower TA means a lower carbon dioxide amount on the left-hand side:

CaO + CO2 <---> Ca(2+) + CO3(2-) + heat

The calcium oxide is bound tightly in pool plaster mostly as 3CaO•2SiO2•4H2O while the above reaction is very much thermodynamically favored to the right (the reverse reaction starting from calcium carbonate is how cement is made in a kiln along with silicates).

The chemistry I've been working on is not new. I've just been putting together existing pieces The latest breakpoint chlorination model (chlorine oxidation of ammonia) is from 1992 and 2000. I also follow current disinfection by-product research, mostly by Ernest "Chip" Blatchley, from 2007, 2009 to present-day.

Richard