We've had our inground pool for three years now and havent ever had any problems with it until this year.
It first started out after the 4th of July where we noticed our pool started to get a little cloudy and we kept losing our chlorine levels. We have 20x44 inground pool with a SWG. We kept "boosting" our SWG, but the within a day or two our chlorine levels were almost zero. Our combined chlorine then started to raise from 0 to .5, so we knew we needed to shock it and assumed we had some form of aglae brewing. We followed the guidlines on this site for "slamming our pool" and everything seemed fine for a week or so. Then we started noticing our chlorine levels again we not holding and kept slipping down again. Our pool remained crystal clear, but we also noticed what we thought was sand on our seems in the bottom of the pool and also on one of our steps. It looked beige in color (like sand), but then was not gritty like sand. Instead it dissolved when we went to sweep it or whipe it up. After doing some reading, we have been treating this like Mustard Algae. Our CYA was 60, so we have been shocking our pool with bleach and getting the FC level to the recommended 36 ppm level. We have been leaving out pool cover open as much as possible to help air it out. The FC has dropped during the day sometimes to around 26 or 27ppm, so we have raised it up again to 36 or a little higher at night. Since doing so, a few days we're no longer seeing the beige substance, but now have seen a black substance in the same areas where the beige was. Is this dead algae? ( I thought it would be white or gray, but this is has been black). Also yesterday we didnt have any residue and we thought we were almost at the tail end shocking this, but now this morning there's a little bit of black residue again, and our cc has raised again to 1.0. Of note: my husband did take out the filter last night to clean it, do you think that has anything to do with it? We started the shocking 5 days ago. Just wondering if were doing the right thing still. Any advice is highly appreciated. Also is it ok if we leave the pool cover on during the day? (and do we need to be concerned about our automatic pool cover having this algae?).
Thanks so much again for you help/advice.