I have read on here about bringing the cya level down by adding water. I will be doing a backwash and rinse today after brushing so will have to add some water. Can I do this instead of adding more bleach to bring FC slam level from 16 to 20?
To answer your question: It generally takes much more water removal and replacement then you can do with just a backwash, then water top off. It would be nice if it did move it that easily though .
As far as the FC level increase: You may Not need to raise the FC level from 16 to 20 anyway. It will just depend on if your CYA is actually closer to the 45, or closer to the 55.
A smaller CYA range would help us be able to advice you on that part better, but for now just continue the same way and at the same level you've been running it at.
You are doing Great!!!! Then once you check the CYA again, IF the CYA reading indicates a need for increasing the FC level you can do it at that time, but there's no sense in doing it now until we are sure. I hope this helps.