Low TA levels, High PH

[DaveD]

I know this is a Pool site, but I have a hot tub and cant find any good advice anywhere else, so I hope you can assist me.

My Total Alkalinity is pretty low, and I cant keep it high. Its currently about 40PPM to 80PPM, and my guide says it should be 120PPM. I add the correct amount of alkalinity increaser, and the level comes up. It stays up for about 2 days, and then drops back down again. I'm using tester strips for the TA readings.

The other wierd thing is my PH levels. My TA is LOW, but my PH is HIGH (about 8.5). When I raise my TA, my PH falls. I thought PH would be low if TA was low ??? I have a Hanna meter for PH & have calibrated it with the buffer solution.

Straight out the hose pipe, my PH is about 8.0, my TA about 120PPM.

Any ideas whats causing this ? The store I bought my tub from has no idea whats causing it. They just say to keep adding TA increaser. But my TDS is now so high I've had to dump the water after only 4 weeks & start again. Please help ! Thanks.

[chem geek]

If you have aeration of the water in the tub, either from an ozonator or from aerated jets, then this drives carbon dioxide out of the water and causes the pH to rise. Higher TA levels only make this problem worse so don't worry about keeping the TA so high. If you keep it at or above 50 ppm this should be fine since it does not sound like you are using an acidic source of chlorine. What are you using for sanitizing the tub?

Richard