My FC does not go below 6ppm. My CC are less than .5 or 0 all the time. But every once in awhile I get a very slight alga along the seam of the wall. I raise the FC up, vacuum the next day and pass the 3 criteria. I've moved the jets around for better circulation and swim every day to move the water around. Run my filter for 4 hrs at night and 3 hrs in the middle of the day. It is covered with a solar cover when not in use. I test regularly and everything is good.
How does this algae grow. The water is crystal clear and has been all season. What am I missing?