I haven't been able to figure this out and the big box pool companies just give me maybes with no definite answer. The pressure of my pump is 30 psi when the filter is in, after the filter is cleaned. Without the filter in, it's still 15psi. When the filter is in, the pool water doesn't even move at all, leading to algae growth, and also, the chlorine tabs don't get enough water flow in to dissolve. It's awful, and I need it fixed, but I don't want to get screwed by a pool company in the process. Any help?