pH keeps bouncing up

[Jtowne99]

Hi, this is our second year of pool ownership. We bought a house last year that had a pool with CYA well over 100 ppm, so we drained it two months ago and refilled. We can't seem to keep the pH down, though, now so I'm wondering if we need to aerate. Here are the stats from a few minutes ago:

pH - 8.0+ (My kit only goes to that)
FCL - 0.6 ppm
Alk - 110 ppm
CYA - 30 ppm
CH - 310 ppm

I double checked to make sure the pH reagent is still good and it is. We were going to add more bleach today as it is a little green until I got the pH results again. We added muriatic acid a week ago and had it at 7.4 ppm. It pops back up over 8 ppm every week, though. Also, We try to keep the pool covered because we're in the windy season here. The temp with the cover on was 85, but dropped to 74 today with it off.

Any suggestions on what we're doing wrong are appreciated.

 

[Richard320]

You have high TA which pushes pH upwards. All you can do is keep adding acid to lower pH. Each time you lower pH, you also lower TA. pH will climb back up, TA will stay down.

You were probably using trichlor pucks last season, which are very acidic, so you didn't realize the pH was constantly rising and simultaneously being knocked back down by the pucks so it looked stable.

You can check pH & TA twice a week (or more if it really climbs) and lower pH to 7.2 each time until it slows down or flatlines, or get aggressive and get it over with in a few days Pool School - Lower Total Alkalinity

 

[Jtowne99]

Thanks. We had the same problem last year with the pH rising all the time using bleach (we never used anything but bleach). We just kept adding muriatic acid though. I didn't bother with aeration then because the CYA was so high from the prior owner that it didn't seem worth it. We knew we had to drain the pool at some point, so just did what we could to keep things sort of in balance. I was hoping with the drain and refill this year that the TA would be lower, but I guess not.

 

[Jtowne99]

Being a newbie and not remembering my high school chemistry, we don't understand what would cause our 7.4 pH city water that we filled the pool with in March to jump up over 8. Is it because of decaying debris that blows into the pool and sits for a few days before we vacuum? We have only swam 3 times this year.

 

[AimeeH]

As Richard said, high TA will cause the PH to creep up. Have you taken a look at the article he linked on how to lower your TA.

Aerating will cause your PH to rise but is part of the process of lowering TA.

 

[Jtowne99]

I just read again about the high TA and decided to test our tap water. It's 110 ppm, just like the pool. Mystery solved. Thanks all.

 

[chiefwej]

High TA in your fill water and high evaporation rates, make it an ongoing battle to keep the TA low enough that the pH is somewhat stable. Ask me how I know.

 

[Jtowne99]

Chiefwej,

Since you're in the same boat, I have a few questions for you. We got it down from 8+ to 7.4 last night after a lot of muriatic acid (was trying for 7.2) and it was back up to 7.6 this morning. Do you aerate or just try to manage with acid? I never got it under control last year and can foresee the same issue this year with our high alkalinity fill water. Also, do you keep yours covered to lessen evap? We do for that and to get the temp up because I freeze if it's below 80 (my husband thinks that's a bit warm, so we have an ongoing issue with the "perfect" temp.) I'm concerned about wrecking the pool cover if I have to dump acid in twice a week, plus bleach, and it defeats the purpose if I have to remove it all the time to do that. I don't know how long it should be left off after treating to prevent damage (if at all).

i also noticed that you have the Heliocol solar heater and would love to hear how that has worked for you. I want one to get the temp up and extend the season, since the cover doesn't heat it up enough in April and May for me.

Jennie

 

[chiefwej]

A few things, for a cover I use a cheap thin solar cover. You need not worry about damage, they only last a couple years and are cheap to replace. I only use the cover to prevent nighttime heat loss during the early season when trying to get up to swim temp. The solar works well to add heat but without a cover you would lose it back each night.

I have high TA in my fill water and have to go through the acid and aeration process to lower it a few times a year, in order to keep the pH more stable. But you need to know how the process works. You need to use muratic acid to lower your pH to about 7.0, then aeration for two or three hours. Then check the pH and drop it back to 7.0, and repeat until you get the desired TA. Most of the change in TA seems to happen when you are aerating water that has a pH of less than 7.2. From your description you aren't lowering the pH enough for it to work well. Don't worry about dropping the pH to 7.0 as that's by definition pH neutral. I buy several two-gallon cases of acid at a time when I'm going through this process, and the pool store probably thinks I'm nuts. But, it works. It usually takes a day or two to get the TA down. Once I get my TA down to about 60 or 70 the pH will begin to stabilize, usually around 7.8. If you need further pH buffering, after the TA has been lowered you can look at adding borates.

To determine how much acid to add, use Pool Math. It will tell you how many ounces to add, then just estimate when pouring. It's too dangerous to actually measure out muratic acid.