Pooldoc suggested the diluted sample for the CYA test to get a more accurate reading of what your CYA really is--if it's over 100, we don't really know HOW FAR over 100 it is, so if you dilute the sample, test, then multiply by 2, we get a better idea of what it really is.

If you're using trichlor tabs, it won't take long to get the CYA levels up, especially if they're in a feeder set at the highest setting. As a rule of thumb, for each 10 ppm of chlorine the trichlor provides, you're also raising your CYA by about 6 ppm. So...it won't take long at all to start seeing it come up.

Very often (and even more often last year!!) you'll see the CYA in a pool drop, sometimes to zero, over a winter if the pool is allowed to go green. There is bacteria related to the bloom that will "eat" CYA and then "poop" ammonia, which on opening takes a huge amount of chlorine to overcome. If you saw your CYA drop, that's likely what happened to it.

Don't hesitate to ask questions--we take the time to answer them because we enjoy being able to help others enjoy their pools--that's what we're here for!