Trouble maintaining PH

[ekrug]

Starting in early April I have been trying to maintain the pH of my pool between 7.4 and 7.6. On 4/7 it was 8.0 and TA was 110. I added 1.5 quarts of muriatic acid and the pH dropped to 7.4. A week later the pH was up to 7.8 and TA was down to 100. I left it like this for a few weeks and then on 4/27 pH was 8.0 and TA 100. I added 2 quarts of muriatic acid and pH went down to 7.4 by the next day. The following week pH was back to 7.8 to 8.0 and TA was down to 90. This cycle repeated several 2 more times. Current levels are pH 8.0 and TA: 70. Since the TA is now low, I don't understand why the pH is high. I am reluctant to add any more acid since the TA is low. Adding sodium bicarbonate to increase the TA seems wasteful since my past experience tells me that when I add acid to reduce the pH, the TA will eventually lower. Something else seems to be at play. Any ideas?

Pool Info
Type: Plaster
Filter Type: Sand
Heater: None
Size: 27,000 gallons
Sanitizer: Sodium Hypochlorite preferred, Calcium Hypochlorite when preferred not available
Test Kit: Taylor K-2006

Last Test Kit Results 6/6/2020
FC: 2.5
CC: 0.0
pH: 8.0 (acid demand 2 drops to 7.4)
TA: 70
CH: 350
CYA: 40
Temp: 85

Last Pool Store Test Results 6/9/2020
FC: 0.93
TC: 1.1 (CC = 0.17)
pH: 8
TA: 73
CH: 276
CYA: 53
Iron: 0.1
Copper: 0.3
Phosphates: 812
TDS: 1200

 

[mknauss]

Welcome to the forum!
Drop pH only to 7.6 or 7.8. It will have little effect on TA. Watch your FC, you are below minimum. Keep in target range based on FC/CYA Levels

Do you have any sources of aeration? Spa spillover, fountains, waterfalls, sheer descents, etc?

I suggest you read ABC's of Pool Water Chemistry.

 

[Holydoc]

ekrug,

Also why are you getting the Pool Store to test your water if you have your own test kit? You cannot trust that the pool store's test is right. You CAN trust the Taylor test kit. Now trust your own testing and post that, bring your FC up to the recommended level, and finally start reading the link that Marty posted. You will gain a wealth of information and learn quickly how to best maintain your pool.

 

[Richard320]

Plugging your pool into poolmath, i get that to drop pH from 8 to 7.6 with TA of 70 will take 20 oz 31% acid.

Scrolling to the bottom, 20 ounces of acid will lower TA by 2.9. You won't even see that change on the TA test.

 

[ajw22]

Welcome to TFP.

What type of pool do you have? Please create your signature with details of your pool and equipment?

TA down to 50 is ok.

 

[ekrug]

First, sorry about the lack of information in my signature. I put information about my pool in the original post: plaster, 27,000 gallons, sand filter, no heater. I didn't explicitly state that is is NOT a salt water pool. I have read almost every article in the Pool School area. I am aware of the low FC level. The pool store test results were from a sample taken in the morning after a day where I forgot to add chlorine. I was concerned about the age of my test kit so I took a sample to the pool store to compare test results. The test report shows the last time I tested was 9/12/2019 so I don't do it often. I test FC and CC daily in the morning and it is usually 2.0-2.5. I add enough sodium/calcium hypochlorite to get the FC level to 5.0. I have sprayers that can cause some aeration but I don't use them much. I have an ozone/UV sanitizing system that aerates the water, presumably with ozone but I doubt the concentration is very high. I remember reading about using aeration to raise pH quickly after adding a large amount of acid to reduce TA. I'm guessing that the constant aeration by the ozone/UV sanitizing system is what is causing the pH to always be high. I could plug the venturi inside the ozone/UV santizing system for a while to see if it has an effect on pH.