alapool,

It's funny (ok, not really ) that they told you your CYA is exactly 100. My pool store uses the same test method and, since my pool was new last year, they ran a lot of tests. They always said it was 100 last year and this year the first test said 50.

Apparently they round up to the nearest 50 because I used Ben's kit for the first time a few weeks ago and my CYA reading was zero. Unfortunately, I wasted a lot of bleach before I figured this out.