Oops, sorry. FC and TC are 20 CC has been no more than 0.5 for last 2.5 weeks. pH I use a probe for aquariums...it's been calibrated recently. I test cl- using a FAS-DPD titration method; CYA, alkalinity, and acid demand I usually do at work (university lab). I have also confirmed cl- & pH levels at work. I am beginning to think that I'm missing something, or my filter is sick.

Thanks,
Stella