Cause(s) of pH rise?

[clintmiller]

This is the end of my first full year of pool ownership. It’s not a new pool, nor has it recently been replastered. I’ve had to add approx 1 gal 31.45% muriatic acid (TA 100) in the last month to keep the pH in the mid 7s.

This is a 30,000 gal pool in North Texas, so it was “open” all winter. I didn’t have to add acid at all last year, after we moved in and started it up. We used it heavily last summer and into the fall. And since then, only occasional spa use.

Is this just normal? I’m definitely new to this, so just trying to learn what to expect. I definitely have been adding chlorine at an expectedly high rate as pollen and other signs of spring land in the pool.

Any advice or something obvious I’m overlooking? Thanks!

 

[Texas Splash]

Welcome to TFP! Most common reasons to see pH increase are:
- New plaster - N/A for you
- An elevated TA; this can vary by pool type and chlorination methods, but if your TA is over 80, lowering a bit may help
- Aeration; if you have a spillover, limit its use
- There's also no need to fight the pH and try to make it stay in the mid 7s. Many pools, especially salt, tend to stabilize around 7.8.

Update your signature with all of your pool and equipment info and it may help with more answers.

 

[clintmiller]

No salt cell here. I guess more than anything, I’m just taken a bit by surprise since it was basically on “autopilot” and didn’t require anything to control pH last year.

Thanks for your thoughts!

 

[CraigChing]

I would recommend using pool math to track your testing over time. It’s hard for you or anyone else to analyze a problem like this without the history of your water test results.

One potential source of a higher TA (which could cause your pH to raise faster) is if your fill water TA changed. Have you always used the same fill water? It would probably help if you understand the reasons pH rises. Maybe reviewing some of the pool school articles could help.

 

[clintmiller]

Yeah- I’m using PoolMath and have been since we’ve had the pool. Fill water is the same- city supply right out of the garden hose.

We had crazy storms blow through last Friday. Probably dropped 1.5” in about 40 minutes. That might explain the 0.4 pH rise over the weekend, but as i mentioned in the first post, this has been going on for a 4-5 weeks.

 

[mknauss]

How did you chlorinate the pool last year and how are you doing it now?

 

[clintmiller]

Liquid chlorine (10% bleach) since October 2020. Pool company that helped while we renovated house was using trichlor. As expected, CYA got a bit high and I’m working to bring it down. It’s 85 now.

 

[mknauss]

So while using trichlor, you did not need to add acid, because you all ready were. Trichlor is very acidic.

Once you stopped the trichlor, and you are no longer in winter, you need to add acid. Very normal.

 

[clintmiller]

I don’t think I put all that together from the pool school section. Very helpful, Thanks!