This problem has been puzzling me for years now. I can't seem to get sustained suction for vacuuming. If you look at the photo, you can see our pool has a simple setup. One inlet and 3 return jets. The pump/filter is located about 29 feet from the inlet. I have a vacuum plate that is on most of the time, and I usually insert the vacuuming hose directly into it. Lately, I've tried removing the plate, and inserting the hose directly into the inlet.
It seems that the problem I have, no matter what configuration - is that I only get about 10 minutes of really good suction off the hose. This happens with both a hand vacuum (on a pole) and a Kreepy Krauly. When you first hook up either, it sucks like gangbusters, but then tapers off. What's strange is that even when I'm not getting good suction from the hose, you can still see water coming in through the pump, and there is water surging out of the outlet jets.
Any help would be appreciated - If I could only have good, sustained suction for 30-45 minutes at a time cleaning the pool would be a much easier task