Tired of pH drift

[spoonman]

Hi folks

My pool is plaster and is about 11 months old. Since the pool was constructed I've had an uphill battle keeping the pH in line. The pH increases about .3ppm per day meaning I have to dose with acid every other day best case.

To compound the problem, I live in Phoenix so my water is full of calcium meaning the pH must be 7.6 or less to keep the CSI in check. Ive continued lowering my TA in hopes this would help. Right now I'm at TA 60 and I'm still having major drift issues.

Recently I purchased a Stenner to use for liquid chlorine. I'm at the point of considering using the Stenner for acid instead since the pH demand is much more onerous. Other ideas are lowering the TA to 50 or adding borates.

Any advice from my fellow TFP squad?

 

[JoyfulNoise]

I live in Tucson and my CH is 1200ppm. I can easily keep my CSI in a good range. I think you may be targeting too low a pH by trying to keep it under 7.6. When it's lower than 7.6, CO2 outgassing is much faster and pH rises more quickly.

I'm at the point where I have to drain and refill this fall but I distinctly remember my lower CH years when I could easily maintain a good CSI and let my pH ride between 7.6 & 7.8.

Can you post a full set of test results?

 

[Frankhugus]

My plaster (Pebble tech) 2 years old and I'm adding about 7 oz MA every other day to keep ph below 7.8. TA is 80-90. Time will tell I guess.

 

[spoonman]

Thanks for the responses. 7.6 is my ideal pH based on keeping a 0 CSI, but I usually don't add acid until I hit 7.8+. The thing is that since the pH jumps about 0.3 daily, if I lower to 7.3, I'm back at 7.9 the day after next. To me this climb seems excessive.

 

[JoyfulNoise]

If you are using manual chlorination, then there's no reason to target an overly negative CSI. You can easily let your CSI get as high as +0.3 without much of an issue.

The rise in pH is not linear. Your seeing a +0.6 rise over 2 days but the rise from 7.3 to 7.6 probably happens within the first 12 hours or so and then the remaining rise in pH takes longer. Dropping the pH all the way down to 7.3 is usually not necessary and just wastes acid.

One thing to look at is aeration. Do you have any sources like water falls or spa spillovers? Bubblers? Are your returns pointed up?

Reducing sources of aeration will reduce pH rise.

Also, have you measured your fill water? What are the pH, TA and CH values of your fill water?

 

[spoonman]

I'm only lowering to ~7.3 because it buys me an extra day. If I lowered to ~7.5 I'd be adding acid daily (bouncing from 7.5-7.8).

My fill water pH is 7.5, TA 150, CH ~450. I have no aeration sources, but I suspect my newish plaster could be a main driver of the acid demand.

 

[JoyfulNoise]

The TA from your fill water is fairly high. Phoenix has high evaporation rates (like Tucson) and so your adding water to your pool everyday that is putting upward pressure on pH. New plaster doesn't help either but it less of factor since a properly plastered pool should be cured within the first 30 days or so and there should be no further emission of calcium hydroxide into the pool water.

I'm not sure borates are going to help you much. It might give you an extra day but not much more than that if your acid demand is as high as you're reporting. Adding an automated acid pump will make adding acid easier but it's not going to reduce your total acid demand or testing regimen. In fact, with an acid pump, you need to more diligently monitor pH and TA as excess acid additions can cause the TA to be reduced too far and then you'll get a pH crash.

No easy answers as that's just life with a new pool. Over winter, the acid demand should drop considerably. Adding a pool cover to your pool, if possible, will stop pH rise altogether.

 

[ryan-california]

Adding a pool cover to your pool, if possible, will stop pH rise altogether.

Matt, how does that work? Solar blanket or rigid, does it matter? I assume due to evaporation stopping.... or way off base?

 

[JoyfulNoise]

Matt, how does that work? Solar blanket or rigid, does it matter? I assume due to evaporation stopping.... or way off base?

Solar bubble cover. Needs to float on pool surface. Yes, it stops evaporation and it reduces the outgassing of CO2 which the primary cause of pH rise. Should rewrite that - it won't completely stop pH rise but it will greatly reduce it. Mine nearly stopped when I used a cover.

 

[ryan-california]

Gotcha thanks. Guess the bubble cover goes back on soon

 

[spoonman]

I do use a bubble cover in the shoulder season so that should help for a few months out of the year. Also as mentioned the evaporation/refill will be much less in the winter.

Unfortunately the summer is very long in PHX and acid demand is still very high for at least 6+ months. I'm considering lowering TA to 50 (down from 60) to see if that helps. If that doesn't work, it sounds like I'll have to add a Stenner or deal with the pH rise each spring-fall.

 

[epro05]

Your signature includes "aerator jets". Aeration will definitely raise pH. Any way to cut them off.

 

[spoonman]

^Very observant. They are on a valve and have been off for over a month.

PS: I like your pool. I take it you'd know a thing or two about aeration

 

[epro05]

Yes I do Those 3 fountains run whenever my pool pump is running (which I try to keep down to 2 hours a day - seems to work for me). But I do have to add MA every few days. My CH is lower so I can let pH run up to 7.8 without causing a CSI problem.