I've got a well system, with a standard 10-inch filter housing between the pressure tank and the water softener.
The filter housing is plastic, and there are shut-off valves on either side. I religiously change the filter once a month, but when I tried to loosen the housing recently to replace the filter, I could not get the housing loose.
I tried some Russian diplomacy but it won't budge. I'm afraid to use too much force because I don't want to (a) rip the housing loose from the wall or (b) mess up the input/output lines attached to the housing.
Any ideas? I guess the nuclear option is to install a whole new filter housing, but I was hoping for a trick to loosen the existing one.