In July while on vacation my chlorine level dropped to 1, and there were light grayish-green patches of algae on the bottom. I SLAMmed and thought the problem was fixed. But since then, if the chlorine drops to 7 or below, the patches re-form. With my CYA at less than 30, I would like to keep the chlorine level at around 4-5, but I can't because of the patches coming back. When I raise the FC level to above 10, the patches disappear.
What kind of algae acts like this? Do I really need to keep my FC above 7 all the time? Maybe I didn't SLAM it long enough?