Some times when I shock for 3-4 days after I get what looks like a black dirt on the bottom of my pool that seems like dust if it were dry. It dissipates with even the slightest water movement. Do others ever have this issue? Could that actually be dead algae? My cc at one point was 6 and now it's 2.5. Not shocking everyday due to aa treatment 10 days ago. Dropped in 2 1/2 gallons of liquid chlorine And that's when it does it. Going to shock again tomorrow night. Pool clear and no staining, but with sand filter it doesn't easily hold this black "dust" for lack of a better word. In the past I always worried it was a broken line til I figured out ur was only when I schocked.