I have a bit of weird situation going on and I "think" I have it figured out but just wanted to confirm with everyone here.
I have a cartridge filter (in my sig), and with the OEM Hayward cartridge clean and pump on high, it runs right at 14 PSI. When it gets to 20 I clean it.
I bought an aftermarket filter (Pleatco) and with it clean and my pump on low, the pressure does not even register (literally, zero). When I switch the pump to high, I get bubbles in the pump chamber and still not very much pressure (can't remember exact reading, but less than 2 if I recall right).
I believe that the Pleatco filter is so non-restricting that on high the pump cavitates and introduces air into the system (bubble coming out of returns also). This DOES NOT happen with my OEM filter on low or high.