As algae is killed by the FC, the FC is converted to CC, which drives down FC and drives up CC.
That's what you said too.
CC is removed by the sun. If the CC isn't dropping though, that means there is still FC being converted to CC. A CC of .5 is just a good barometer that everything is done, but there has to be enough FC in the pool to kill algae and continue the process. So if FC is low, a low CC may not mean anything. And in conjunction with the OCLT it's even more of a sure bet that all is well.
That's what you said too.
CC is removed by the sun. If the CC isn't dropping though, that means there is still FC being converted to CC. A CC of .5 is just a good barometer that everything is done, but there has to be enough FC in the pool to kill algae and continue the process. So if FC is low, a low CC may not mean anything. And in conjunction with the OCLT it's even more of a sure bet that all is well.