High Pressure!

I recently cleaned my cartridge filters (pentair model...only about a year old) and the pressure dropped as expected to 12-15 psi. Within a week, however, it spiked up to 22 psi (near the cleaning level) so I took it apart thinking the filters got blanked somehow. They looked pretty clean so I am stumped.

In possibly related news, I know I have something wrong with the check valve on the discharge line to my spa because it drains into the pool when the pump is off. I have tried to take out the check valve to inspect it, but I can't get the unions free. Maybe something is lodged in there blocking flow and keeping the check from seating?

I also wonder if I may have filled the piping on the clean side of the filter with gunk when I cleaned the filters first. The standing water level in the filter is slightly higher than the lower filter outlet pipe so some of the dirty water drained into the clean side when I removed the filter.

Any other ideas or things I should check? Also, any guidance on how to remove the unions on the check valve so I can inspect/replace?