Hello I have a 48 sq ft DE filter and 1.5 HP pump, the pool is older than 4 years but we have owned it for 4 years and have never had this problem. This year we replaced all DE grids and made sure we had New O rings. My pool is very green right now. Thick dark green. We added the appropriate amount of chemicals and the grids are brand new. We added the 6lbs of recommended DE for our filter size. When I turn the pump on everything works fine for 15-20 min and then the pump basket which I can see through the clear lid half fills with air and the flow to pool return lines almost stops it's still very slowly coming out and when I put my hand over the intake line there is barely any suction. So took the whole filter lid off and hosed down the grids and added new DE and the same issue happens again. Then I backwashed it and it worked again for about 20 min and the same issue. This went on for hours with me just wasting tons of DE. I could no longer keep this up so I put the pool on recirculate just to keep the water moving and to distribute the chlorine and green to clean algae killer. With the pump on recirculate there is no issue. The pressure coming out of the return lines stays strong and the clear lid on the pump shows me the basket is full of water and no big bubbles in it. I don't understand what is going on I know with a. Dirty pool I will need to backwash frequently but every 15-20 min makes me think something else is going on.