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Some truths about pH and TA


waterbear
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THE MAIN CAUSE OF pH RISE IN A POOL OR SPA IS OUTGASSING OF CO2.

THE HIGHER THE TA (CARBONATION IN THE WATER), THE FASTER CO2 WILL OUTGAS AND THE FASTER THE pH WILL RISE.

THE HIGHER THE AERATION OF THE WATER (OZONE SYSTEMS, SALT WATER SANITIZER SYSTEMS, AIR INJECTORS,  AERATION FROM YOUR JETS, 24 HOUR CIRCULATION ON HIGH SPEED, ETC.) THE FASTER CO2 WILL OUTGAS AND THE FASTER THE pH WILL RISE.

THE LOWER YOU PLACE THE pH THE FASTER IT WILL RISE (YOU ARE CONVERTING MORE BICARBONATE IONS, WHICH IS WHAT WE MEASURE AS TA,  INTO CARBONIC ACID, ESSENTIALLY CO2 DISSOLVED IN THE WATER.

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Your TA depends on what sanitizer you use. For liquid chlorine, lithium hypochlorite, and calcium hypochorite which are net pH neutral (alkaline on application, acidic reaction when they sanitizer) or a salt water system and/or ozone which increases aeration then you want your TA low, 50 to 70 ppm is usually a good range, for dichlor and trichlor, MPS, and 2 or 3 step bromine activated by MPS or diclhor which are net acidic (acidic on application and sanitizing) then you want your TA much higher to prevent your pH from crashing from the continued application of acid. Recommend range is 100 to 120 ppm or even possibly a bit higher.

For 2 or 3 step bromine activated by chlorine then you want to run your TA in the 60 to 80 ppm range in most instances.

In all cases running the pH higher (above 7.6 for chlorine and above 7.8 for bromine) will increase pH stability since the lower you put the pH the faster it will rise. Also adding a secondary borate buffer in the 30 to 50 ppm range will also increase pH stability in addition to the other benefits of adding borate to your tub or pool.

Realize that other factors come into play such as the amount of aeration so there are no hard and fast rules.

Bottom line, if you pH is rising too fast and is not stable and you are trying to maintain your pH above 7.6 or 7.8 then your TA is too high. Lower it.

If your pH (and TA) keep dropping too fast or crashing to dangerously low levels at the low end of your testable pH range then you TA is too low. Raise it.


 

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On 5/16/2022 at 10:11 AM, waterbear said:

Your TA depends on what sanitizer you use. For liquid chlorine, lithium hypochlorite, and calcium hypochorite which are net pH neutral (alkaline on application, acidic reaction when they sanitizer) or a salt water system and/or ozone which increases aeration then you want your TA low, 50 to 70 ppm is usually a good range, for dichlor and trichlor, MPS, and 2 or 3 step bromine activated by MPS or diclhor which are net acidic (acidic on application and sanitizing) then you want your TA much higher to prevent your pH from crashing from the continued application of acid. Recommend range is 100 to 120 ppm or even possibly a bit higher.

For 2 or 3 step bromine activated by chlorine then you want to run your TA in the 60 to 80 ppm range in most instances.

In all cases running the pH higher (above 7.6 for chlorine and above 7.8 for bromine) will increase pH stability since the lower you put the pH the faster it will rise. Also adding a secondary borate buffer in the 30 to 50 ppm range will also increase pH stability in addition to the other benefits of adding borate to your tub or pool.

Realize that other factors come into play such as the amount of aeration so there are no hard and fast rules.

Bottom line, if you pH is rising too fast and is not stable and you are trying to maintain your pH above 7.6 or 7.8 then your TA is too high. Lower it.

If your pH (and TA) keep dropping too fast or crashing to dangerously low levels at the low end of your testable pH range then you TA is too low. Raise it.


 

Hi, I hope I'm not abusing your knowledge with my constant questions but here goes...

I have a vacation rental which has a hot tub. It uses Ozone and the frog@ease dichlor/mineral sanitation system. As you can imagine, keeping a solid pH balance can be a challenge and the sanitizer always worries me. I charge $80 if I come to find a noticeably damaged tub from not bathing first. That works about 60% of the time and it's really obvious when people showered beforehand. Granted, I check on the tub after two uses but I'm always worried.

I have seen some properties that have users dump a non-chlorine oxidizer into the tub after every use. Would you advise this? I usually refill the tub after two weeks so I don't think CYA content would get unreasonably high but I could easily be wrong.

Finally, I have been looking into automatic pH feeder systems. The one from Hannah instruments seems to work with its own buffer and pH solution. Would that be a better solution than shocking the tub after every use?

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