To correct the last few posts .... CYA does in fact breakdown due to the chlorine in the pool. But, it is very slow, maybe lowering by up to ~5ppm per month. So it may take a few months before you can actually see a difference in the test. Although at the same time splash-out and backwashing will lower the CYA as well.
Bottom line, it should not change very fast, but you should not ignore it for months at a time. At least test and adjust at the start and middle of the season.
Bottom line, it should not change very fast, but you should not ignore it for months at a time. At least test and adjust at the start and middle of the season.