pH keeps creeping up

[frankcav]

Since opening the pool this year I need to add muriatic acid weekly (about 1 to 2 quarts) to keep the pH at 7.2-7.4 range or else it tends to gravitate to 7.8-7.9. I don't recall adding this much acid last year. My current numbers are:

FC 3.0
CC 0
pH 7.4 (after adding HCl today)
TA 70
CYA 30
CH 40

Inground vinyl 24,000 gallons

My question is would increasing the TA to around 100 or adding a second buffer like borates to about 50 help stabilize the shifting pH.


Thanks in advance,

Frank

[KurtV]

Increasing the TA would exacerbate your pH rise problem. Lowering your TA to 60 or even 50 will help some and the borates may help also. See the "Great Tetraborate Experiment" thread for more on that.

[frankcav]

Thanks for the input... will probably add borates.

Frank

[Jakebear]

I'm having the same problem (pH Creep). DH says it is normal since we add bleach automatically (pump) but I read one of Richards Posts about the chemistry where he showed that the chlorine reactions caused negligible change in pH (I think the thread was titled "Rising pH levels"). Anyway I've been adding about 15-20 oz per day to keep it in range.

Here's my numbers:

Water temp 85 F
FC 3.0
CC 0.0
TA 100
pH 7.6 (added 11 oz Muriatic yesterday)
CYA 22
CH 140 (but who cares with a vinyl liner)

Bleach Pump add about 20 oz 3% [EDIT: not 6% as originally stated] bleach per hour while circulator pump runs (8 hrs/day)

crystal clear, no algae, no problems, just have to dump acid every day

I'd like a better explanation if there is one.

[chem geek]

My question to Frank and Jakebear would be whether you have any water aeration features in your pools, such as waterfalls, spillovers (negative edge or pool/spa combo), fountains, showers, aerating jets, etc.? Also, Jakebear uses a bleach pump, but what source of chlorine does Frank use (SWG or bleach/chlorinating liquid)? Are you having a lot of rain (the splashing of raindrops provides a lot of aeration)? Are there any chemicals you are adding to your pools other than chlorine and acid?

As was pointed out, increasing the TA level only makes the problem worse and would require you to add more, not less, acid over time. With your vinyl liners, you can lower your TA level to 50 ppm without a problem and should find some improvement. Also, setting a target pH of 7.7 instead of trying to fight to maintain a lower pH will also help (for Frank, I would try that before lowering the TA further from 70; for Jakebear, you can certainly lower your TA to 70, see how it is, or lower it further to 50 as needed). Turning off water aeration features (if possible) will help. Using a pool cover should also help.

Adding Borates should reduce the frequency of acid addition (i.e. it will take longer for the pH to rise), but will not change the amount of acid you need to add over time (i.e. you will need to add more acid less frequently for the same net acid/time result to bring the pH back down). The main advantage of the Borates is that it gives you an additional pH buffer so that you can lower the TA level even further than you would normally do if the Borates weren't present. Note, however, that the borates do not have much capacity to handle a drop in pH so with low TA you need to be careful about any acid addition beyond that which you carefully monitor -- for example, CYA is acidic and Trichlor is very acidic.

This chart shows the relative carbon dioxide outgassing rates at various TA and pH levels. This is proportional to the quantity of acid you need to add per time. It is not an absolute amount since that depends on the amount of aeration, whether the pool is covered, wind, etc. This chart shows the relative rate of pH rise at various TA and pH levels. Though a lower TA significantly lowers the rate of outgassing, it is also less of a pH buffer so these somewhat balance out though the net result is a lessening of pH rise. You can see that going from 70 to 50 will help just a little, but maintaining a higher pH of 7.7 helps even more.

Richard

[Jakebear]

Hi Richard, We love your commentary an knowledge.

DH is fcfrey, you two have kicked around a lot of emails over the last year and we have learned a lot from you (and others too).

We have a fresh water pool with a pump like they use on a dialysis machine. He rigged it so the pump runs whenever the pool pump runs. It works well but he says he might have to add an acid pump to it??????

Any way we have had about 2" rain as thunderstorms over the last 2 weeks which has kept up with evaporation and rug rat splash out. Since we have a DE we do not back flush very often (just bump). There are no fountains etc. We have not added anything other than chlorine and acid for 6 or 8 weeks except a bit of CYA (DH wants it up to around 30 to try to cut chlorine consumption a bit)

We do not have trouble with TA ---- Just the pH. It's not a big deal but since I don't have to lug jugs like last year -- maybe I'm getting lazy. Either way all last year on BBB (before the chlorine pump) we never had to add acid so I'm wondering ------ was-sup????