Air in lines and unstable pressure after cleaning filter
We got the water from green to less green and milky - so I think we're winning against the algae. But we noticed DE coming into pool via returns when adding some to skimmer. Opened up the filter (Pentair FNS 48) and found the grids in bad shape and the manifold cracked. Got new innards for the filter and installed today. I opened the relief valve on top of filter and turned pump on set to backwash until water coming from bleed valve. All went fine and then set to filter. It's running but there is air coming out of one of the returns (for 8 hrs now). Also, the pressure is sort of surging. It is a bit unsteady in the 12 psi range but then surges up to 20 or so and I can hear the pump surging. It seems to have calmed down somewhat but not as smooth as it was before I opened the filter.
Any advice? Also, I believe there's air in the pump filter as I can see water drops on the inside of the lid. I tried turning pump off and opening filter pot to fill with water which seems to work but later I see it is not full of water.
Pool: 40K gal, 20' x 50', 8' deep - In-ground / Concrete w/ Zeron epoxy paint ● Pump: Hayward Super Pump (2HP) ● DE Filter: Nautilus FNS - 48 ft^2 ● Valve: Pentair SM-20-2; SWG: Pool Pilot with CC-15 cell