Risks with high alkalinity?

[Rangeball]

Jeez, it would help if I read a post more thoroughly! Rangeball, I would still be interested to know what your calcium level is in your pool and, if you don't mind testing it, in your fill water as well (unless you recently refilled your pool). My guess is that the CH is rather low which is good in your case and explains why you aren't seeing scaling nor cloudiness.

Unfortunately, a guess is all I have to go with as well. I don't have the capability to test CH (wanted to order Ben's kit but was waiting for the issues to be resolved, having good luck with OTO kit so figured I'll put off a full kit until next season). I live in a small town, and our one pool store screwed me big time last season and I refuse to do any further business with them. Our fill water is supplied by our local municipality, I'll call them to see what their last water test shows.

In the meantime, I thought I had this issue resolved. Previously I had been aerating WHILE trying to lower PH, didn't work and I got nowhere. Now I lower PH then aerate, and alk was staying low at 130-40ish, PH holding steady. I added about 3" of fill water (ph 7.2 alk 320) last week before my youngest daughter had a swimming party, and after the party my PH was back up to 8. Looks like I'll have to attack it again, and it will probably be a normal part of my pool maintenance life as long as we have such high alk fill water...

[EDIT] I just read Tom's (waterbear's) post which surmises you have high CH -- at any rate, now I'm really interested in your pool's CH reading. [END-EDIT]

Richard

I thought waterbear = Evan?

[chem geek]

I try to keep it at 7.2-7.6 to maximize the effectiveness of the chlorine. Which, BTW, I can keep at 1.5-2ppm (EDIT - 30ppm CYA) and stay clear blue. If you'll notice in the pic above, this pool is cut into a hill and I think the deep end is cooled by the ground, so it stays close to 84 degrees F, which might be helping.

So here are the "calculated" numbers for your pool, just so we can see if theory matches reality or not.

At pH 7.2, the CO2 outgas rate is 45.7 which is very high; at 1.5 FC your ppm HOCl is 0.023; at 2.0 FC it's 0.032

At pH 7.6, the CO2 outgas rate is 17.2 which is possibly near "stable"; at 1.5 FC your ppm HOCl is 0.019; at 2.0 FC it's 0.027

So this implies you are having a strong tendency of rising pH. The theory would say that if you started at 7.6, then you would see a much smaller pH drift upwards and would use less acid. In fact, somewhere in the range of 7.6 to 7.8 could be a place where you would be about stable with little or no perceptible drift.

As you can see from the ppm HOCl numbers, they don't change that much with pH (due to CYA acting as a buffer for HOCl). You are at the "low" end of Ben's table range so proabably what he considers to normally prevent algae though he has given me worst-case examples with algae that were at about 0.05 ppm HOCl.

Even if you let yourself drift to a pH of 8.0, your FC of 1.5-2.0 would mean a ppm HOCl of 0.017 to 0.024 which is lower, but not by much. You could just increase your FC to be between 2.0 and 2.5 (or 3.0) and you'd be in pretty much the same shape.

I think the fact that CYA acts as a chlorine buffer to offset the effects of pH is a useful piece of information from the theory that would allow you to operate at higher pH with proper disinfection and algae prevention. If you are willing to take a small chance to try it out, I think it would be worth it given your high alkalinity and CH situation.

Now, as for the saturation index, yours is 1.0 and since you have no evidence of scaling nor cloudiness, that shows that the index can get quite high (we still don't know how high) before scaling is an issue. By the way, do you know your level of TDS? A higher TDS lowers the saturation index. Just based on your alkalinity and CH your TDS has to be at least 860.

Richard

[Rangeball]

Called City Hall and had them fax over the most recent drinking water quality test report. Didn't contain a reading for Calicum.

Called the Water plant directly, they don't test for calcium

Does the 5/6 way drop test kit at Walmart test CH? They have some there for $12, I was thinking about getting one to see where my CYA is now that I used 4 8oz tri-chlor sticks while I was gone for a few days.

[chem geek]

I thought waterbear = Evan?

Yes, waterbear is Evan's login name. [EDIT] I don't know why I mixed up the name with Tom -- my brain fart. [END-EDIT]

I wouldn't get discouraged with your situation. What I'm trying to work through, along with Evan, is the possibility that you can operate at a higher pH and not worry about your high alkalinity as much. If you try to go to a pH much lower than 7.8, then you will be "fighting" the pH rise due to the outgassing of carbon dioxide and you will be using lots of acid. If instead you let yourself operate in the range of 7.8 to 8.0, then you can still be safe by keeping your chlorine levels about 15% higher than Ben's chart.

Since you are not seeing scaling nor cloudiness, there should be no problem with your running with the high alkalinity. The ideal situation would be for you to outgas CO2 to lose alkalinity at about the same rate as your fill water adds it to fill up after evaporation. You can just monitor your alkalinity over an extended period of time since it should move quite slowly (assuming you start with a pool alkalinity the same as your tap water).

So, bottom line, don't try to fight the situation you've got (high alkalinity) and instead accommodate it via a higher pH operating level.

Richard

[chem geek]

Called the Water plant directly, they don't test for calcium

Do they test for total hardness and is that in the report? I have a calculator that can approximate the calcium hardness based on the typical 4 to 1 Calcium to Magneisum ratio (typical well and ground water -- mountain spring water is closer to a ratio of 2.6 to 1).

The formula is Calcium Hardness (ppm CaCO3) = Total Hardness / 1.412 (for a ratio of 4 to 1 and other conversion factors)
[EDIT]Sorry for the wrong factor the first time[END-EDIT]

Richard

[Rangeball]

Richard, thanks.

Initially I'd read Ben's "operate at high ph" article, and planned to do so. However since my OTO kit only reads up to 8.2, I decided not to until I had a proper test kit. I assumed once I got my alk down, PH would be fairly stable, and I'd only have to adjust when I added fill like you said, which is where I am now.

I'll try to get current readings for CL, PH and Alk tonight and add them here tomorrow. I need to get another gallon of acid I'm sure.

Just got a call back from the water plant. They had looked in their records and found an entry from 1975 when the city put 3 new wells in (we're still using them) and the CA reading was 62ppm. Our town sits on top of a huge aquifer, and I don't see much evidence looking around that calcium scaling is a big problem (lot's of ag fields using irrigation rigs, etc.).

I'll look at walmart and pick up their OTO kit if it tests CH.

[Rangeball]

Do they test for total hardness and is that in the report? I have a calculator that can approximate the calcium hardness based on the typical 4 to 1 Calcium to Magneisum ratio (typical well and ground water -- mountain spring water is closer to a ratio of 2.6 to 1).

The formula is Calcium Hardness (ppm CaCO3) = Total Hardness / 2.497 (for a ratio of 4 to 1 and other conversion factors)

Richard

Nope

As this was a drinking water quality report, I'm sure they only tested for the required contaminants.

[jenpen400]

When I filled our AGP a year ago CH was 210 and ALK was 320. I was able to drop the ALK down to 110 but it is much harder to push down from a high number. Once I got the Alk to 220 it was easier. I know how you feel add acid, arate Alk goes down now add water to make up for evaporation and back up it goes. I found that just putting the fountain on low and keeping the ph around 7.4 or lower the alk just keeps creeping down without as much evaporation. Now my alkalinty is fine and my CH is 340. Oh well I guess thats another thread.

Hope this helps
jennifer

[waterbear]

I'll look at walmart and pick up their OTO kit if it tests CH.

It does but it has some issues....many people, including myself have found that it doesn't always work correctly...a workaround that I have found is to keep adding drops of the first reagent until you get the pink-violet color instead of a yellowish color. I have done this and cross checked with both Ben's kit and Taylor's and it is in the ballpark.

[chem geek]

When I filled our AGP a year ago CH was 210 and ALK was 320. I was able to drop the ALK down to 110 but it is much harder to push down from a high number. Once I got the Alk to 220 it was easier. I know how you feel add acid, arate Alk goes down now add water to make up for evaporation and back up it goes. I found that just putting the fountain on low and keeping the ph around 7.4 or lower the alk just keeps creeping down without as much evaporation. Now my alkalinty is fine and my CH is 340. Oh well I guess thats another thread.

Hope this helps
jennifer

Jennifer,

I just want to understand clearly. Are you now at an alkalinity of 110 or 220? Is the evaporation less because you've got the fountain on a lower setting? So now you have a balance between losing alkalinty through the aeration (and adding acid to restore the pH) and gaining alkalinity from make-up water for evaporation. Is that right? So your alkalinity is stable, but aren't you adding a lot of acid frequently to keep your pH down? I suppose that may be the tradeoff necessary.

Evap. --> Make-Up --> Alk. Up
  ^                       V
  |                   Fountain
Alk. Down                 V
pH Down <---- Acid <---  pH Up

Is that your cycle?

Richard