I have a Hayward Perflex EC75 filter and a Superpump 2 HP pump. The pump is new, replacing a 1.5 HP pump. My inground pool has 30,000 gal. I get good flow into the pool for about 15 minutes, then it drops almost to nothing. I've completely cleaned the filter. The poor flow happens with the filter has no diatomaceous earth or has the correct amount. There shouldn't be anything clogging the inflow or outflow, and if there was it seems I wouldn't get good flow at all as opposed to poor flow only after 10-15 minutes. The pressure in the filter builds up quickly and is likely limiting the flow rate. Bumping the filter helps only briefly. It doesn't seem like the air release valve on top of the filter would be an issue, as it probably is functioning fine and any air likely would just get pumped into the pool anyway. The pool water is dirty (I am just opening the pool now and am still killing algae); would this lead to pressure buildup in the filter (it doesn't seem like it, as the filter is clean). I had similar problems with the 1.5 HP pump, and thought that a stronger pump might help (it didn't). Any thoughts or suggestions?