Apologies for the vague subject, but my problem doesn't really condense to a one liner very well.
I've got a several year old 2 or 2.5 HP single speed pump, mated to a less than 1 year old Pentair FNSP60 DE filter. I previously had a sand filter, which was very forgiving of my sometimes lax maintenance. I tend to let some green in, especially when it's early spring but still too cold to swim.
I realized quickly that the DE filter will clog quicker and need flushing, but lately, I've had an odd problem: within a day or two of flushing/recharging, I'll see that the water isn't flowing after the pump has been running for some time. When I go to the pump, it's almost like it's cavitating. There's water in the filter basket area on the pump, but there's air , too, and they're just swirling around, but not really flowing. Filter pressure gauge reads very low (less than 10 lbs).
At this point, I can stop the pump wait a few minutes, then restart, at which time it will resume good flow. Filter gauge reads anywhere from 23 to 26 psi or so (fresh charge baseline is 20). After an hour or less, we're back to the light/no flow.
Any ideas? I swear I don't remember this behavior last year, seems like it'd keep going with progressively less flow until about 30 psi, at which point I'd flush and recharge. Maybe my impeller is having a problem?