The filter is way above water level (IG pool). I just purchased the house last year. The filter has ran about 9 PSI with fresh DE. A few months ago it creeped up to 20 PSI, I back washed, put in new DE still 20 PSI. Then I cleaned the grids & replaced 1 of them, down to 18 PSI. I am at a loss here. I think I may drill and tap some more holes for more gauges. I want one right at the discharge of the pump, so I can see what the pump is doing when I am in recirc. This will tell me if it is a filter problem or return piping.
I believe that part of the problem is the liquidator. When the pump shuts off, the level in the liquidator drops introducing air into the pump. (I have the liquidator piped into the drain of the pump). I am looking into installing a solenoid valve so the line on the liquidator will close when the pump is off.