dkhedmo writes:

OK, so the pool is now full of what may or may nor be softened water.
(New to us house, first time pool owners, pool more than 3 and less
than 10 yrs old.) When the water level got high enough to start
entering the skimmer, the cartridge filter started leaking from where
the top and bottom meet. When the water was high enough to turn on the
pump, I did so just to see what would happen and water gushed out from
the filter in every direction possible. So I turned it all off.

Tighten the screw(s) that holds the 2 parts together.
If you don't know how, post brand/model.

If that doesn't work, disassemble, check for misplaced or
worn gasket and fix or replace.

If you're going to call a service company every time something
goes wrong with the pool, get used to waiting.