High alkalinity & normal ph relationship in a covered pool

avspin

Gold Supporter
Jun 3, 2015
195
Reno, NV
Pool Size
18000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
I’ve had an issue with high alkalinity. I’ve had a few posts about it.

A little history, I keep my pool covered all the time. A few years ago, I found my alkalinity at about 180 and ph 7.5. I asked how to lower alkalinity only and found that it’s tied to ph and I can lower it with Muriatic acid but that would also lower the ph. So, I used liquid acid and lowered ph to 6.8 and alkalinity to 150. Then I would run all my fountains 24/7 and turn the returns up to splash the water which, in theory raises ph only. This only works until ph reaches about 7.2, then I would have to lower again with acid and start over with this cycle until it was in balance.

I tried this method for a month without any success. At suggestions here I just gave up stopped worrying about the alkalinity outlier.

Fast forward to this year. Back in May, my pool cover ripped and ordered a new one. With covid and Texas it took 7 weeks to get but with a nineteen-year-old system, more stuff needed replacing like the dog shifters and reels. Which also took time to get.

During this time, I had no cover for three months. I had to add water about 2+” every 4 days due to evaporation. I turned up my SWG from 25% to 80%, The intelliph from 7% to 30%. Had to keep an eye on salt and cya and added as needed. I tested every 2-3 days and had it dialed it. What I noticed was my alkalinity had dropped to 80-90 which was much better.

Now that it’s covered again, I’m in the process of lowering the SWG & intelliph back to pervious levels, slowly, based on testing. And I’m seeing my alkalinity inching up again, today 130.

So, it seems keeping my pool covered raises alkalinity. I can’t find any posts or info on the web about the correlation. Any expert on chemistry has any insight?
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
44,424
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
Keeping the pool covered for extended periods restricts the out-gassing of CO2. That keeps the pH low.

As long as your CSI is controlled and you do not see scale flakes coming off the SWCG, I would not worry too much about the TA.
 

avspin

Gold Supporter
Jun 3, 2015
195
Reno, NV
Pool Size
18000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
That's been my attitude about the high alkalinity, don't worry about it. All my other stuff is perfect, the CSI is .03 today.
This was more of a "hmm" question to ponder. Mostly for information and education.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
44,424
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
When the pH does not rise, you cannot add acid. The TA will rise until the equilibrium is achieved between the pH, the TA, and the CO2 that is in the water.
 
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