Quick pH rise

[nickmick]

Hello-

This is my second season on this pool. It's brand new, built last June. Closed and opened by builder. Salt/Cartridge filter/Vinyl/Coverstar autocover/~33k gallon (20 x 45 with 6' sunshelf). I'm in the Milwaukee area.

This thing has been crystal clear all last year and this. I've been real happy with it and it's been hands free. The only issue I have is the pH tends to rise "quickly", which, I realize, I actually have no context for what is normal. Basically, I'm adjusting weekly. For instance - this last Saturday (4 days ago), pH was 7.6. Added acid to get it to 7.3. Right now, 4 days later, pH is back to 7.5. I've added over a gallon of acid this month, and I haven't used it much in May (I'm in Wisconsin remember).

Salt - 3300 ppm (avg)
Chlorine - 1.5 ppm (I have the standard Rainbow 78 test kit - it just gives me a chlorine number), generally correlates to a 680 mV ORP reading.
TA - 100 ppm
CYA.....0ppm

I know. I asked the builder about it. His response was, if you feel like you need it - add it. He's never used it in his own pool, or pools he manages, and doesn't have a problem. I'm probably going to not add it unless I start to have an issue. He has just advised me to keep pH in range, keep chlorine in the 1.5-2 ppm range, TA in the ~100 ppm range, and leave it. The pool has been nothing but crystal clear ever since he built it. I don't know if the lack of CYA is affecting the acid rise or not.

I just wanna know - is the pH rise rate normal, or not? I don't have an issue adding a few pints of acid a week, I just wanna know if this is expected.

 

[IceShadow]

Howdy neighbor! I’m over in West Allis.

So - we need info to offer advice, if we can. If you can fill out your signature like mine, it would help us out. My main questions would be:

- How are you testing your water? Most test methods people use before they come here are unreliable, and can result in bad advice. We advise using dropper-based tests to know what your levels are, as it’s reliable and repeatable. EDIT: Just noticed the Rainbow kit. I’m not familiar with it but a quick search shows it’s similar to the Taylor, but with an OTO test instead of an FAS-DPD test. Might be worth getting that separately to supplement.

- What pool surface do you have? Vinyl, plaster? EDIT: And reading fail here too, you mention vinyl.

- You mention salt - are you chlorinating with a SWG?

You’ll find we do things differently here from most of the pool industry. Low FC unbuffered from the sun can vanish on you and leave you with an unsanitary pool. Instead we monitor our CYA levels and make sure we keep our FC in line with it, due to a relationship between CYA and FC that most of the pool industry pros tend to ignore.

 

[nickmick]

Hey Dustin. I'm actually up in Ozaukee Co. Nice to meet you. Yes I'm using a dropper kit, using a SWG, and vinyl.

I know I will get the CYA recommendations but is that causing my (what I'm thinking is) quick pH rise?

Thanks,
Nick

 

[IceShadow]

The normal industry recommendation of 80-120ppm TA is based on using trichlor pucks. They're acidic, and so you need additional TA in the pool to buffer against crashing the pH of the pool with the acidic pucks.

SWG (or liquid chlorine) is pH neutral. (The pH does rise a bit when the fresh chlorine is added, but when it oxidizes or burns off to the sun, the pH returns to what it was.) So with higher TA, aeration, off-gassing, etc. will cause pH to rise.

Don't stress about your TA too much, though. It will cause your pH to rise, and you'll add acid to bring down the pH (we recommend muriatic acid as dry acids include sulfates that can accumulate in the pool and be dangerous to equipment, especially heaters). When you add acid to lower the pH, you'll lower TA as well. You'll need to know what your TA is when you add acid because higher TA means more acid is needed to bring the pH down, but eventually your TA will drift down and settle. My pool likes it about 60 TA, and that's where the pH stops rising. You do want 50 TA minimum to buffer against unexpected pH crashes.

If you really want to push your TA down, you can purposefully aerate the pool to make the pH rise and add acid, sort of accelerating what will happen naturally. But unless your CSI is really high, which it likely isn't in Wisconsin as we turn over our water pretty regularly, you don't need to force it and can just let it come down over time with acid additions.

I do recommend you read some articles here about how we keep CYA and FC for chlorination. You can make the call on if you want to follow our methods or not. I like the way things are done as recommended here, because I feel like I have a handle on the pool and confident that it's safe to swim in and won't have an algae outbreak without breaking the bank.

ABCs of Pool Water Chemistry
Recommended Levels

Feel free to ask any questions you want about why the chem levels are recommended as what they are.