Cloudy water has three usual causes: early algae, a filter that isn’t keeping up, or calcium coming out of the water. Testing tells you which.
1. Early algae
Test free chlorine (FC) and combined chlorine (CC). If FC is below the minimum for your CYA, or CC is above 0.5 ppm, algae is probably starting before it turns green. Run the SLAM method.
2. The filter
Clean or backwash the filter if the pressure is high, and run the pump longer each day. A sand filter clears water slowly; give it a few days.
3. Calcium
When pH and calcium hardness are both high, calcium can come out of the water as a fine haze. Lower pH toward 7.2–7.4 with acid. Right after adding cal-hypo or soda ash the water can also look milky for a few hours: give it a day with the pump running.
Fix chlorine and pH before you try a clarifier or flocculant. They hide the cause instead of fixing it.