Liner Pool Care

[waterbear]

Waterbear, I read on here I think that the stabilized tabs have a pH reading of 2 or 3. The Cal-hypo tabs have a pH reading of 11 or something. Someone correct me if i am wrong.

If i keep adding stabilized tabs they will decrease my pH, and i wont be able to add acid to reduce the TA.

Next week when I go there I will drain about 3 or 4 inches from the pool.

Just a caution, we are getting into advanced chemistry here that is probably better in the china shop. Mods, please move if you see fit.
The effect of the pH drop from trichlor are cumulative over time. 1 lb of trichlor wil drop the pH by only about .5 or .6 and that is not going to make a big difference in TA at all. To lower TA enough bicarbonate has to be converted to carbon dioxide and that has to be allowed to gas off (which then causes pH to rise again).
Also, part of the pH drop is from the reaction of the chlorine when it oxidizes something. The reaction is slightly acidic. Unstabilized chlorine sources such as cal hypo and liquid chlorine are esentially pH neutral in use. Initial addition raises pH but then the acidic readtin neutralized the rise. Stabilized chloirne sources (trichlor and dichlor, which are very acidic and slightly acidic respectively) have a net acidic reaction over time that eats up TA as it keeps bringing the pH back up, the buffering effect talked about.

Bottom line is this. If you are going to use a stabilized chlorine source (CYA aside) you need to have a higher TA than if using an unstabilzied chlorine source. In fact, the last CPO manual I browsed through recommended TA of 100-120 for stabilized chlorine and 80 -100 for unstabilized chlorine, chlorine gas, and SWGs.

Now a TA of 210 is high but the question you need to ask is how stable is the pH. IF the pH rise is staying within acceptable limits between your service visits then don't worry about it and just add acid as needed. IF your pH is always too high when you test the pool on service calls then work on lowering the TA.

With a CYA of over 100 you are gong to need to drain and refill (or run higher FC levels with an unstabilized chlorine to compensate) but if you are dealing with high TA fill water then trichlor is certainly something to consider using for a period of time after the drain and refill, as long as you monitor the CYA. This also depends on the type of filter. If it is a cart or bump type DE then I would not use trichlor but if it is a filter that is backwashed on a regular basis (sand) then each backwashing will have a small dilution effect on the CYA levels as you remove and replace water and makes using trichlor a bit more managable.