I tested my pool this morning and the FC was zero. I used the pool calculator and added the appropriate amount of bleach. I waited 4 hours and tested again it's still at zero. The TA is also very low. Everything else was at the appropriate level. I did recently add DE to my paper filter after reading that several people had positive results clearing up a murky pool this way. The pool is looking much clearer than it was but I'm puzzled as to why the FC fell to nothing. We have one of those floating chlorine things in the pool. Any help is much appreciated!