pH too high and struggling to reach pH 7.5

Vegas Mike

Member
Mar 30, 2019
18
Las Vegas, NV
Have needed to add about 2 cups / day muriatic acid to approach pH goal of 7.5. Fill water is pH 8.0, and using a peristaltic pump dispensing 24oz/day 10% bleach. The 2C acid is about 8 times what Pool Math says, so makes me wonder what I'm doing wrong. My pH measurement tool is an Apera PH700 meter, calibrated with pH 7.0 standard before each measurement. When researching bleach, supposedly only 4% excess NaOH at this concentration, so I don't think that is the culprit. Waterfall 8" high does not add much agitation, but runs 8 hours / day. FC is 2ppm before daily addition. CH is 200, TA 110, CYA 30.
 

Richard320

TFP Expert
LifeTime Supporter
Jan 6, 2010
22,069
San Dimas, CA (LA County)
I just plugged your numbers in, and poolmath wants 15 ounces -- just under 2 cups -- of acid to lower the pH. So that tallies with what you're adding. Which makes me question why you posted, "The 2C acid is about 8 times what Pool Math says." Better check the volume you have entered up above. Something ain't right.

2 cups a day is reasonable, until you work that TA down to 60 or 70, when it may stabilize enough for you to only need acid whenever you top off the water. Note that as TA goes down, that the amount of acid needed to effect a certain pH change also goes down. So you can't make a blanket statement that 2 cups of acid will lower pH .5, because that won't stay true for much longer.

I suggest you speed the process up and shoot for 7.2 pH when you add acid. It'll take a lot, but it'll drive the TA down faster. Overall, the amount of acid you'll need to lower the TA a certain amount will remain the same. It's just over how long a period you want to spread it. Daily additions can get pretty old pretty fast, which is why we even have an article explaining How to Lower TA

In other observations... you ought to raise that CYA to 50 or 60 because the Vegas sun can be fierce and will destroy all your chlorine in a hurry. Also, if you can slow the flow over the waterfall, or reduce the total hours the pump is running, the pH rise will slow down. I run my filter 2 hours a day, and my spillover spa gets maybe 20% of the return flow. It's enough to keep the algae at bay.
 

Vegas Mike

Member
Mar 30, 2019
18
Las Vegas, NV
I must not be using Pool Math correctly. Just entered the pH 8.2 measured today, target pH 7.4, and it said to add 2.7oz of 29% muriatic acid. I added 24oz, and will probably see a pH 7.8 tomorrow morning. Pool volume looks correct at 10,000 gallons. Are there other settings (that I must have incorrect)?

But a relief to know 2C/day not unusual. Thought from the negative comments sent to folks contemplating a peristaltic pump to add acid that adding this much daily must be excessive. I'll focus on getting the pH down. I'll admit a certain lack of consistency in how often I check pH. It rained an inch at my house Monday! In Vegas!

If I'm able to maintain free chlorine that is never lower than 1ppm and virtually zero CC, does 30ppm CYA matter? Just means using lots of bleach, right? Had CYA above 400 and FC above 15 before I took over from my pool service who used trichlor, so I'd like to keep CYA low for now. Would like to avoid draining/refilling again anytime soon.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
23,062
Laughlin, NV
I get you need to add 25 oz of 28.3% - have to admit I have never seen 29% MA.

Be sure you have your TA entered into PoolMath. That is used in how much acid is needed to drop the pH.
 

Vegas Mike

Member
Mar 30, 2019
18
Las Vegas, NV
Skipped the TA section on acid addition, and that was the problem -- Thanks! And good to remind me of the CYA to FC relationship. My FC actually has stayed above 2ppm which is consistent with 30ppm CYA, but I incorrectly thought 1ppm would have been OK. And on my muriatic acid container it says 29% HCl (and 71% inert ingredients). Hmm.