I'm completely at my wits end with this situation and I have tried everything.
So with a clean DE filter, main pump basket, and skimmer baskets the pressure gauge and water return output is normal. After 30minutes pressure gauge increases and output decreases.
I have checked for clogging in skimmer lines, replaced suction side 3 way valve and suction side flapper valve. Thinking it was my pool pump (making noise), I replaced it as well....but the problem remains. Also spa drain slowly at time and constantly have to diver water to fill flapper chamber to to spa water feature.
Bother skimmers get good suction independently, but with one open and the other is opened I get air/lack of flow to the pump and pressure drops.
Only thing I can think is main drain has a clog?