Well I was helping a friend out this week. He has a newer Hayward DE filter. It was filthy so I sprayed it down with a hose and got all the gunk of. The pressure gauge was reading 35-40. After cleaning off the filter (but before adding any DE) it was still reading 35-40. The water flow and suction in to the skimmer is greatly reduced. There's a valve to go to recirculate and water flow is great when it's in that position but when I go back to running water through the filter the water flow is very weak. He's got algae and I think we need better water circulation to help combat it. Any ideas? When I add the DE is it going to make that much of a difference to the filter pressure?