Trying to understand my PH rise

[Schadenfreude]

Hi. My PH is puzzling me. We had our plaster pool drained and acid-washed in April. Since them I have been following TFP methods pretty religiously. Our pool water is beautiful, clear and clean. But...

My PH keeps rising. This is somewhat expected with the SWG, but I was putting in two gallons of MA a week. So, I tried borates (which are great). The only effect on PH is that I now need twice as much MA to bring the level down - instead of putting in half a gallon every other day, I now put in a full gallon every other day. I don't have any fountains, slides or any other source of aeration.

Anybody have any insights?

FC - 5.5
CC - 0
PH - 7.5
TA - 60
CH - 425
CYA - 80
Borates - 50
Salt - 3400

ETA: fill water TA - 140, PH 8.0 (could I just be getting that much evaporation?)

 

[Texas Splash]

ETA: fill water TA - 140, PH 8.0 (could I just be getting that much evaporation?)

Woo! That's a lot of acid. How old is your pool/plaster? One gallon of acid for 50K = about .6 of adjustment in pH. I suppose it's possible. My acid usage has increased as well by my own standards to keep-up with evaporation and fill water. That on-top of the fact you have a miniature lake for a pool. That's a good size watering hole you have there. Twice the amount of churning and aeration from water movement along with that fill TA.

Have you ever considered a cover to help cut-back on evaporation? Pool size/shape permitting of course.

 

[Schadenfreude]

With the borates the gallon only knocks down the PH by 0.3, not 0.6 - I expected the borates to slow down the PH rise, so I would add a gallon twice a week rather than half a gallon four times a week, but that didn't happen. The plaster is 18 years old.

The pool is an odd shape, making a cover problematic. We tried just throwing the big sheet of bubble wrap on it, but the prevailing winds just bunched it all up on one end of the pool. We spent a ton of money on solar rings, but the quality was abysmal. We had to return about half of them right away because they had air leaks. The rest failed after one season.

 

[Jimrahbe]

I suspect with a pool that big you also have some pretty good sized water features. What are they, and how often are they running?

Also, where are you trying to hold your pH level? Mine stays at 7.8 for a pretty long time, but if I try to lower it to 7.2 or so, I'd have to add acid every other day.

Jim R.

 

[Schadenfreude]

 

[JoyfulNoise]

What is your pH target?

By the way, an acid washed pool will act a lot like a newly plastered pool as the acid washing etches away the calcium carbonate layer and exposes some of the calcium oxide in the deeper plaster layers. This can lead to rapid pH rise until the plaster "cures" again.

 

[Schadenfreude]

I suspect with a pool that big you also have some pretty good sized water features. What are they, and how often are they running?

Also, where are you trying to hold your pH level? Mine stays at 7.8 for a pretty long time, but if I try to lower it to 7.2 or so, I'd have to add acid every other day.

Jim R.

No water features. Just a swimming hole. I've tried to see if it stabilizes at higher levels. If it does, it's higher than 8.2.

- - - Updated - - -

What is your pH target?

By the way, an acid washed pool will act a lot like a newly plastered pool as the acid washing etches away the calcium carbonate layer and exposes some of the calcium oxide in the deeper plaster layers. This can lead to rapid pH rise until the plaster "cures" again.

That makes some sense. Any idea how long it might take to slow down? It's been three months so far.

My target is anywhere from 7.5 to 7.8. When it goes over 7.8 I knock it back down to 7.5.