A low TA is actually not a problem and will help reduce the amount of acid you need to add to keep the pH where you want it. The only issue is that it reduces the saturation of calcium carbonate in the pool, but that only matters if you have a plaster/gunite or similarly surfaced pool (or any exposed grout with tile). For a vinyl pool, for example, it doesn't matter. For fiberglass, you should have some Calcium Hardness (CH), but don't need to be at full saturation (we think). If you have a plaster pool, then it's easy to compensate for the saturation through a slightly higher pH target and/or a higher CH level.
If your CYA level is low (say, around 30 ppm), then I wouldn't worry about the TA until it gets to 50 ppm. I would still keep it above that, but you should find that it drops rather slowly over time. And just be careful about adding any acid to the pool -- it will take less to move the pH due to the lower TA (and that includes acidic sources of chlorine such as Trichlor and Dichlor as well as non-chlorine shock).
By the way, do you have water aeration features such as a waterfall, spillover, fountain, air jets, etc.? Or do you get a lot of summer rains (raindrops splashing cause aeration)? Pools are intentionally over-carbonated, just like a carbonated beverage (though obviously not THAT carbonated!) so outgas carbon dioxide to the air and that process causes the pH to rise (with no change in TA). Then, adding acid to lower pH also lowers the TA. You may also find that having a pH target of between 7.5 and 7.7 will help compared to trying to maintain 7.4.
Richard
