Rising pH?

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andreww

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Mar 3, 2016
5
Los Angeles, CA
Hi all- I have a relatively new pool (8 weeks since start up). It's a 6,500 lap pool with an integrated spa and infinity edge. It's pebblefina plaster finish. I have an ozonator and a triclor tablet feeder.

Mostly my levels are pretty good, but no matter how much dry acid I add my pH keeps rising above 8.0. I'm worried about raising the temperature in the spa with such a high pH because of calcium scaling.

Latest readings:
FC 1.0 (ozone is the primary oxidizer)
CC 0
pH 8.0
Alk 120
Calc 190

I was able to get my pH down last Sunday to 7.5 by adding 36.0 oz (weight) of dry acid (two doses, mixing with water first, slowly feeding in front of the pool return jet).

Since then, the pH has been stubbornly above 8. I've added 14.0 oz of acid twice but haven't seen a change in pH when I test the next morning.

Any thoughts?
 
andreww said:
Hi all- I have a relatively new pool (8 weeks since start up). It's a 6,500 lap pool with an integrated spa and infinity edge. It's pebblefina plaster finish. I have an ozonator and a triclor tablet feeder.

Mostly my levels are pretty good, but no matter how much dry acid I add my pH keeps rising above 8.0. I'm worried about raising the temperature in the spa with such a high pH because of calcium scaling.

Latest readings:
FC 1.0 (ozone is the primary oxidizer)
CC 0
pH 8.0
Alk 120
Calc 190

I was able to get my pH down last Sunday to 7.5 by adding 36.0 oz (weight) of dry acid (two doses, mixing with water first, slowly feeding in front of the pool return jet).

Since then, the pH has been stubbornly above 8. I've added 14.0 oz of acid twice but haven't seen a change in pH when I test the next morning.

Any thoughts?
Click to expand...

Hi Andrew, welcome :wave:

I think what your going to find here at TFP is that we are a chlorine based pool forum and we do not put a lot of stock in pools that have disinfection systems setup like yours. If you search our forum discussions you will find a lot of hard science on here that disproves the usefulness of ozone in residential outdoor pools (ozone can sometime be useful in indoor pools and hot tubs but only in very rare circumstances). We also DO NOT believe in using trichlor tablets for regular chlorination as they build up stabilizer (cyanuric acid, or CYA) in your pool water which is very detrimental over the long term.

I don't want your first post to devolve into an argument since we hope to help everyone have a better pool experience but you'll find little support for the type of setup you have.

I can offer advice on two fronts that are your main concern - pH rise.

You have a new plaster finish and it is totally normal for new plaster surfaces to take anywhere from a year to 18 months to fully cure and stop contributing to pH rise. The plaster can be a source of alkalinity in the pool water (especially from calcium hydroxide) and that just takes time for it to come under control. Secondly, you have a pool with LOTS of sources of aeration (spa & infinity edge). Pool water is intentionally over-carbonated (your TA is 120ppm) and any form of aeration causes CO2 to outgas from it. The process of CO2 outgassing causes the carbonate alkalinity (mostly bicarbonate ions) to shift equilibrium and generate more CO2 to replace that which is lost from aeration. That process of bicarbonate converting into aqueous CO2 consumes a proton (H+ ion) and thus raises your pH. Adding lots of acid exacerbates the problem because low pH shifts the carbonate equilibrium more towards aqueous CO2 allowing for higher concentrations of CO2 in the water and thus increasing the rate of outgassing. The only way to arrest this is to keep your alkalinity low and your pH in a narrow range of 7.6-7.8. You can also cover your pool water surface with a bubble cover that will help arrest CO2 outgassing.

As for acid, we really recommend you use muriatic acid instead of dry acid. Dry acid is sodium bisulfate which leaves sulfates behind in your water. Over time and with extensive dry acid use, you will build up sulfates in the water which can be detrimental to plaster surfaces AND can cause calcium sulfate (gypsum) scaling if the pH and CH get too high. Muriatic acid, while a bit more difficult to handle, is much better to use in a pool as it only builds up chloride in the water.

I hope this helps and I do hope you will search our threads and see what we're all about.

Matt
 
Welcome! :wave:

Curing plaster, high Alkalinity, and a lot of aeration are all going to conspire to drive the pH way up. Expect to need a whole lot of acid the first six months at least. Muriatic acid is probably the best bet, because the dry acid adds sulfates. Check this post by Chemgeek for an explanation.

Once the TA is driven down by the acid, the rate of pH rise should slow down some.

You didn't list your CYA levels. You're adding CYA with every trichlor puck, so it's important to know that number in order to maintain adequate free chlorine. The ozone may do well to oxidize organic wastes - dead skin, snot, sunscreen, and the rest - but it doesn't sanitize. Without knowing the CYA level, you don't know if the 1.0 FC you have is sufficient to kill pathogens.

Have you been to Pool School? Start with Pool School - ABCs of Pool Water Chemistry
Then browse around a little and check out some of the other articles. I find the Pool Chemistry section to be very informative.
 
Thank you for your in depth reply!

I've switched to muriatic acid. I didn't think aeration would have such an effect on pH -- I'm only running the edge for an hour a day to cycle the water in the trough, and I haven't used the spa.

Every day that I get the pH down in the 7.5-7.6 range, by the next morning it's >8. I suppose that's normal? My alkalinity is staying stable around 110-120.

Should I just keep administering acid?
 
That's some very excessive acid demand.

Your TA is way too high. If you are past the 30 day plaster startup stage, then you need to start lowering the TA. I would suggest you go down to 80ppm TA and see what happens. If you are adding any alkalinity increases (baking soda), stop. Use the process laid out in Pool School for lowering TA.


Sent from my iPhone using Tapatalk,16k gal SWG pool (All Pentair), QuadDE100 Filter, Taylor K-2006
 
Andrew,

Looking at Banditig's link it says:

The acid/aeration process to lower TA:
1. Add acid to lower your PH to between 7.0 and 7.2 (this also lowers TA)
2. Aerate until PH rises to around 7.6 (the only way to raise PH without also raising TA)
3. Repeat steps 1 and 2 until you reach the desired TA.

I believe that the most important part is not allowing step 2, to get back above 7.6 before adding acid again....

When I initially tried this process I'd add acid and lower pH to 7.0, and then I'd check it the next day and it would be back to 8 something, so I'd do it again, etc.. I never seemed to get anywhere.

Then I started testing every couple of hours after adding acid and making sure that I never let the pH get above 7.5. Doing this, my TA came down and pretty much has stayed down and my pH stays around 7.5./7.6 for several weeks and sometime months at time, before TA and pH start to slowly move back up.

Jim R.
 
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