If fc + cc + tc why is my reading lower which is more important.
I'm guessing that was just a type-o. FC+CC=TC So, if your FC is 3 and your CC is 0 then your TC will also be 3. The CC is important because if it's more than .5 then you need to bring your chlorine up to "shock" level (depends on your CYA level) to get rid of the "useless" chlorine.