Why add CYA at all?

[aquarium]

Hi All,

Thank you for this forum. I've spent some time reading through and have a couple of questions.

We just moved into a house with a 15,000 in-ground concrete pool. Although I've never had a pool before, I keep a freshwater planted aquarium, so the water chemistry stuff is very familiar. We're just outside of San Antonio so lots of alkalinity and a relatively high pH, both easily (EDIT: Well, maybe not the alkalinity) controlled with muratic acid.

The pool had -never- been drained before, so to get back to a known starting point it is now a few inches from being refilled. It has an auto-chlorinator and I have a little more of the Bioguard 3" trichloro-s-triazinetrione tablets. I'd rather stick with tablets (I'll probably go generic) since adding bleach every day is a non-starter for a variety of reasons.

My question: Since a pool consumes 1-2ppm chlorine each day anyway, and I can run the filter on a timer to add that during the sunny part of the day, and 1-2ppm works best at near-zero CYA, why do I need to add CYA to get it up to 30-40ppm? Why not just let it build slowly using the tablets, and then do water changes to keep it low?

Thanks,

Tom