I had a lot of trouble with this gray dirt building up rapidly on the pool floor last season. A few times I found little water bugs living happily in the pool even though the chlorine was good or a bit high. Sweeping the walls and floor make the pool very cloudy. I tried yellow out and shocking, etc... I also tried all-type algae killer copper sulfate. Also had the pool tested for phosphates and was told it was low. Now I'm not even sure what this is... is it just pollen dust?