pH Constantly Rising

[Ryano2121]

I can't figure out why my pH keeps rising. I get it down to 7.4-7.6 but then the next day or two it goes up to 7.8. I'm putting so much acid in. Everything else seems good. Any thoughts?

FC 3.5
TA 70
CYA 70
pH 7.8

 

[Husky25]

Are you aerating in any way? Even unintentionally? Where are your returns pointed? If toward the water surface, consider pointing them straight out or down.

 

[chem geek]

Do you have aeration sources such as a waterfall, spillover, or a fountain? If you can turn any off then see if the pH rise is slower.

Instead of bringing the pH down to 7.4, let it go to 8.0 and then bring it down to 7.6 or 7.7. You should use less acid that way and it may settle down in its rate of rise when it gets to higher pH. If it's carbon dioxide outgassing causing the rise, then it is slower at higher pH.

If you are using an off-brand of bleach or lower-quality chlorinating liquid then these can contain too much excess lye that can have the pH rise over time.

Finally, what is your Calcium Hardness (CH) level? Hopefully your saturation index isn't so low that your plaster is degrading. Do you see any Calcium Nodules?

 

[Ryano2121]

No aeration, I have a spill over but it's been off for a long time.

I have a SWG so I don't add any chlorine.

CH is 320 but that's the same as my fill water. I don't see any nodules.

I will try letting it go up.

 

[chem geek]

I didn't know you had an SWG since that was not in your signature. SWG pools tend to rise more in pH in part due to the increased aeration from the hydrogen gas bubbles. Also, if you have a short pipe run between your SWG and the closest return, there may be undissolved chlorine gas outgassing. If you point that return more downwards, that might help. Finally, you can consider adding 50 ppm Borates to your pool. Though that may not lower the amount of acid you need to add, it should reduce the rate of pH rise and will help reduce scaling in your SWG cell.

 

[Ryano2121]

Sorry, I thought I changed my signature before I posted.

The swg is on 20% and it's a long line to the closest return so I don't think it would be the bubbles.

I'll add Borates and see how it does.

Thabks!

 

[chem geek]

It can still be hydrogen gas bubbles since those will still aerate the water and not dissolve. It's the chlorine gas that in a longer pipe run should fully dissolve so wouldn't be outgassing. Anyway, the borates should help at least slow down the rate of rise. You should still target a low TA and higher pH as that is the fundamental source of pH rise from carbon dioxide outgassing.