I have a TF-100 test kit that is going on its second season. I'm nearly out of CYA reagent and when I used it today it never registered any CYA at all. Seems strange given that I ended the season around 90 doesn't it? Is the reagent bad perhaps? While we're at it, do I need to replace all of the chemicals in the test kit? I still have quite a bit left to get me through this year. . .