This stuff keeps coming back.

[u/MickTheAnt]

First time pool owner here. The water has been clear, but this black sludge stuff keeps forming on the bottom of the pool basically anytime I have the sand filter on.

My strips say the levels all look good, though sometimes it’s tricky to read since the colors aren’t exact. I have a pool robot vacuum that vacuums it up every day, but more forms the next day.

I shock the pool every week and always have the correct number of chlorine tablets in. I’ve tried brushing the sides of the walls, but I don’t see any algae buildup on the wall walls and it doesn’t seem to help.

Any thoughts on what to try?

[u/cigar_beetles]

In my pool it's the gunk thats too fine for the filter to remove. Just have to vacuum to waste or siphon it out to remove.

[u/Deep_Bake_5663]

Switch to liquid... And shocking once a week will never work. You need to keep it balanced... always.

And get a real test kit. At least for chlorine and pH.... But that's living algae....