Increasing pH

[drskorzy]

Hi All!

Have a curious situation with the pH steadily increasing in my pool. First...details:
Gunite / in-ground 15000 gallon pool. Built/installed in the mid '80s (came with the house we bought!)
Attached jacuzzi with return water that spills back into the main pool
CYA = 50ppm. TA = 70ppm FC = 2-4ppm (TC matches usually as I keep on top of it) Liquid chlorination only. Hardness: Ca = 300ppm (what our tap water hardness is at)
Filter/pump on 7-8hrs/day depending on season. Cartridge filtration. Manual pool chemistry only.
Use a Taylor DPD kit for regular chemistry testing. Hach 7 in 1 strips for "quickie" testing.

I hope that's enough info.. but I've always had an issue with this pool's pH increasing in short time. I use muriatic acid to adjust down to ~ 7.4, but within ~7-9 days, the pH always increases up to >8.0. I have no idea why... and its driving me crazy because I have to dump acid into the pool on a regular basis. $$$!

I have read somewhere that "aeration" systems (e.g. artificial waterfalls, sprinklers) de-gas CO2 which can lead to pH increases. The intake from the pool is from a "creepy crawly" vacc system and skimmer. Filters.. but return water goes into the jacuzzi where it pulls in air and creates the "bubble" return.. overfill spills over the dam between the jacuzzi body and main pool, back into the main pool body. Is this the potential reason?

I was thinking of switching water return to the main pool for a week or so and testing the pH as an experiment, but that would also mean the jacuzzi is not receiving filtered water. Thought I'd probe the brilliant hivemind here on possible solutions.

What sayeth' you?

-J

 

[ajw22]

The aeration from your continuous running spa spillover is raising your pH. That is probably your primary problem.

What is the pH and TA of your fill water?

Try lowering your pH to 7.6-7.8 when it hits 8. The lower you go on your pH the faster it rises. Plaster pools tend to like being around 7.8.

Please put details of your pool in your signature. This a plaster pool? What automation do you use to turn the spa on and off?

Most automation system have a spa spill over mode that you can use to turn on the spillover for two or three periods during the day to refresh the water.

 

[drskorzy]

I've not tested the fill water except for pH (~7.2) and Ca (300ppm). Its a timed pump operation. Just a pump intake at the vacc and simmer, through the filters, then return with aeration into spa and spill over back into the main pool. Filter on at 9AM- Off 5PM. Don't have the option to customize spillover. Its either aeration spillover into the jacuzzi > pool or return without aeration into the main pool with no jacuzzi filtration.

 

[ajw22]

Are you using strip to measure pH & TA & CYA?

 

[drskorzy]

No. Taylor test kit for this. The strip kit's pH seems way off from the taylor kit, but believe the phenol red liquid test kit results.

 

[beautifulpool]

I've not tested the fill water except for pH (~7.2) and Ca (300ppm). Its a timed pump operation. Just a pump intake at the vacc and simmer, through the filters, then return with aeration into spa and spill over back into the main pool. Filter on at 9AM- Off 5PM. Don't have the option to customize spillover. Its either aeration spillover into the jacuzzi > pool or return without aeration into the main pool with no jacuzzi filtration.

Hi dr S, I agree with everything mknauss added in above posts.
Because Your pool and my pool sound very similar, I thought to ask, is there a plumbing option to split the flow, After the water flows thru your filters, into both the main pool body & into the spa. I lived here a full year before I realized that I had the option (by adjusting the Jandy valves) I could control How much water ? flowed & where it flowed -thru the angle of the Jandy. You may not have that option ....
I still leave my waterfall on full blast, as well as my spa fountain (personal preference of course)
I don’t have to use very much chlorine anymore, because I don’t use stabilized chlorine anymore, It takes less chlorine, because the chlorine i add is free to kill and Sanitize. Because I used to use di-Chlor and tri-chlor, I never used to need to add acid.
I now add acid.
If you add the cost of Muriatic Acid, which I now buy regularly, to the 100’s Of dollars i saved this summer (by NOT buying stabilized chlorine)... I’m HAPPY to buy a jug of acid
I come out WAY ahead.
It used to go like this
the more stabilized chlorine I used, the more chlorine I had to add, because my pool kept turning green......which kept increasing the amount of chlorine needed to be purchased and added, which then caused my pool drains
Which then caused 500 water bills and mosquitoes, and start up chemicals ....not to mention the cost of renting drain pumps from Home Depot and power sprayers.... paying for it -and having to do the labor -
Yeah
Im happy to pay for the jug of Acid
I hear the beautiful sound of a waterfall as I pour my muriatic acid into the pool .... )
Don’t know if this helps any
Blessings

 

[drskorzy]

Hi all. Thanks for the suggestions! Exceptionally helpful! I never really realized it before, but the return water valve is a Jandy valve. I turned it so roughy 50/50 returns to the jacuzzi and pool. This was enough so the jacuzzi return doesn't pull air fast enough to aspirate, so its a gentle "whirling" return. I adjusted pH to 7.5 and let it do its thing for four days. By now, the pH would easily be >7.8 normally, but tested it this morning... a still, stable 7.5! Unexpectedly, the FC was 4ppm when I left Thursday, and it would have dropped to 2ppm by now, but its still ~4ppm, so I think the aeration was also driving off chlorines (TC is also ~4ppm). I can always turned the valve to full jacuzzi return when we want bubbles, and back to its "maintenance" position for daily filtration. Thanks again!

 

[ajw22]

Aeration does not effect chlorine.

Glad you figured out your pH issues.