My pool loves low TA

[BillyBumbler]

When I try to hold a TA of 80, my PH tends to rise faster requiring more frequent acid applications, which brings the TA down to around 50-60...where my pool seems happy and the PH holds a good level much longer??

[chem geek]

This is normal behavior if you have high aeration (or low pH or high TA). What is the pH you are targetting? Do you have a waterfall, fountain, spa jets or other aeration feature? Do you have a salt-water chlorine generation (SWG) system?

Also, what is your CYA level and Calcium Hardness (CH) level (if you have a plaster/gunite/tile grout pool)? With that info, I can tell you if you would be running into any trouble with your low TA plus other options, though your pool might be fine as it is.

Richard

[BillyBumbler]

It's an 18000 gal. inground pebbletech finish pool. There is a rock waterfall that I have set to run for 5 minutes every couple days to keep the water in the recesses from getting algae. Yes it is a SWG system. I keep the CYA at between 40-50ppm and the salt level at 2600-3200ppm. Calcium is at around 250-300ppm. FC always around 3 and CC always at 0. Water looks beautiful. In the past I've used baking soda to get the TA back up which resulted in the need for acid to reduce PH, which in effect lowered the TA. Kind of a Catch-22 situation. It could be that I use to much acid? I like to use enough to get the PH between 7.0-7.2 so that I go go a few extra days without checking.

[chem geek]

The main problem is that you are trying to maintain a low pH of 7.0-7.2. Why is that your target your pH? Normally, you would target 7.4-7.6 and that will be much easier to maintain as there will be less carbon dioxide outgassing (and pH rise) at that pH.

[BillyBumbler]

Well not really trying to maintain it that low. Since the PH is always on a steady incline I set it there to give me more time before another acid dose. I add acid at 7.8-8.0. Is this all wrong?

[chem geek]

Well, it's not "all wrong", but adding acid to get down to 7.0-7.2 will cause the pH to strongly rise from that point. The rise in pH will slow down as the pH gets higher so setting a target of 7.4 or 7.5 would be better. At the lower TA, you won't see the rise in pH being as rapid and won't have to add as much acid. If you decide to stick with the low TA, you might want to bump up your calcium hardness (CH) a bit closer to 400 ppm though that is not essential (your water is a little more corrosive with the lower TA and having a higher CH compensates for that).

I suggest you take a look at this thread and consider adding 50 ppm Borates (Borax) to your pool. This should allow you to lower your SWG output (since the Borates will kill algae so less chlorine gets consumed) which will lower the tendency of the pH to rise. The SWG generates not only chlorine, but also hydrogen gas and these bubbles pull out the carbon dioxide from your water and that causes the pH to rise. This is why you see less of a problem at lower TA, because there is less carbon dioxide in the water at lower TA (think of the pool as a carbonated beverage!).

What is the recommended level of CYA that your SWG manufacturer says you should have? Is it 70-80 ppm? We have a current controversy as to whether a high CYA of 80 ppm makes the salt cell more efficient. The problem is that it is easy to add CYA and not easy to get rid of it. So using the Borates is probably a better bet.

Richard