I'm using a Sta-Rite PLD50 DE filter to filter my 24' round Aquasport above-ground pool. Everything was new last season. This year, from the start, I've been noticing what I think is de on the bottom of the pool after over-night filtering. Most of the time my Dolphin vacuum takes care of removing it. Still, this shouldn't be happening. I recently cleaned filter after four weeks from start-up. I added pre-measured 6 lbs of de & started-up again. Water pressure entering pool is great & pressure on gauge is about 95 psi. What could be causing this & what can be done to correct?