You probably shocked without balancing chemistry first.

Probably. Pool shock kills algae and bacteria, but if your pH, alkalinity, or calcium hardness is out of whack, the water stays cloudy even after filtering.

Think of it this way: shock is a sledgehammer, not a scalpel. If your pH is over 7.8, chlorine becomes mostly ineffective. You’re just wasting shock. Same goes for high calcium hardness — that creates a milky haze that no amount of filtering fixes.

Also, dead algae particles are tiny. A sand filter might not catch them until they clump up. Run the filter 24/7 for a day or two. Backwash when pressure rises. And vacuum if you see debris on the floor.

Get a reliable test kit (not strips) and fix pH first — 7.4 to 7.6 is the sweet spot. Then shock again if needed. Cloudy water is usually a chemistry problem, not a filter problem.