I opened my pool two weeks ago to get it ready for memorial day weekend. It cleaned up nicely after several shock treatments. But in the middle of the bottom of the pool, there is a few black looking spots. I thought black algae but not too sure. When I brush it is only a cloudy form in the water. Not even gritty. If I vaccuum on waste, it disappears temporarily, but is back again the next morning after circulating through the night. What am I dealing with?
It probably is a black algae outbreak, which can be very resilient. You may need to brush a chemical (black algae treatment) right on the affected area to break down the base algae which is not being affected from regular brushing. Also make sure your filtration is reaching this area (water moving there). A stagnant area can be reason for recurring algae as well.