TA and acid tug of war

[GeorgeG]

I have a 15,000 gallon pool under a screen enclosure in Florida built in 1986 and resurfaced in 2007 with a quartz finish by Florida Stucco. I am allergic to chlorine so the pool is sanitized by an ion system (copper and silver anode, no salt) which itself does not affect ph. We also shock every week with unstable liquid chlorine (plus manual liquid acid to bring ph back down) which flashes off by the next day, no stabilizers and no chlorine tablets. No additional chemicals are added except powdered sodium bicarbonate for TA manually and liquid muriatic acid for ph by dosing machine.

Everything in the pool pushes the ph up - liquid chlorine additions and the cement/quartz walls. I measure the ph with the Hayward dosing controller, an Extech electronic ph probe, and a liquid test kit. TA measurement is by liquid test kit. If I don't do anything, the ph goes above 8.0 in less than a week. The ion system does not do well with high ph as the ions come out of solution and stain the walls blue/green. Also of course, the chlorine shock effectiveness is much lower with a high ph as well. The ph was constantly drifting above 8.0, scale had formed on the walls and the scale got stained by the ions. A dosing system was added to keep ph at 7.4 which the system does very well. The issue is the ridiculous amount of TA increaser and acid that goes into the system every month to keep the TA above 70 and the ph down to 7.4. Recently I arbitrarily reduced the TA target to 50 and the TA and acid chemical cost dropped at least in half. The pool was drained and acid washed today to remove staining and scale and is refilling as I type this.

I know that the role of TA is in part to stabilize ph but mine never fluctuates per se, it only goes up and goes up even faster if I try to keep TA above 70. In a sense, keeping TA above 70 only makes my ph more unstable. I have lowered chemical costs but will I have any other problems with a lower TA target as long as I keep the CSI between -0.5 and +0.5??

BTW, I am involved in a new pool with the same finish and same system. We decided not to turn on the ion system and just do a higher level of chlorine shock every week and the water is nice and clear with no staining or scale problems. The TA/acid tug of war was the same so I also lowered the TA target to 50 in that pool as well with an equivalent reduction in chemical cost.

Thanks,

George

[chem geek]

Why are you not using any Cyanuric Acid (CYA) in the pool. It not only protects chlorine degradation from the UV in sunlight, but also significantly moderates chlorine's strength. Your pool is not properly disinfected in between your weekly shocks with chlorine. Metal ions do not kill pathogens quickly (see this post) and copper ions by themselves do not kill fecal bacteria.

As for TA and pH, TA is a SOURCE of rising pH due to carbon dioxide outgassing. It is not just a pH buffer. So it is completely understandable that a lower TA has less of a pH rise. Do you have sources of aeration in your pool such as waterfalls, spillovers, fountains, etc.? Aeration drives off carbon dioxide more quickly causing the pH to rise.

You can have the TA be kept low and compensate the saturation index by having a higher Calcium Hardness (CH) and you won't need to worry about a 7.7 or 7.8 pH if you get rid of your metal ions, but unfortunately that will require diluting the water or using regular metal sequestrants.

With your new pool, again, a once a week shock is not sufficient for a disinfected pool. I suggest you read the Pool School to learn how to properly maintain your pool.

[GeorgeG]

I maintained my pool old school for over 30 years with great success after some initial trial and error in the 80's. 15 years ago I became severely allergic to many chemicals and I was unable to use my pool (among other things) for years. I replaced the water and switched to this system about 10 years ago and was able to start using my pool again. I have never had any problems with pathogens or infections going on ten years now and everyone who looks in the pool remarks as to its extreme water clarity. The pool sees very light activity, mostly me and my wife.

I am goint to lower my TA target to 40-50 and raise my ph and CH levels to recenter the saturation index near zero. Does anyone else know of a reason that with a saturation index near zero, a lower TA will cause any problems?

Thank you,

George