Sorry.. Cl = Chlorine FC = Free Chlorine

For your purposes, virtually the same thing.

If I follow what you're saying, you tested 15ppm last night, then added 1.5 gal Clorox (4.5ppm). Test this morning - 15ppm. So you consumed around 4-5ppm Cl.....is that right?

The fact that your water is not where you want it is still your driving factor...keep the Cl in there.

Another helpful additive that hasn't been mentioned in a while (and we all need some of this) is POP (pool owner patience)