it did help with keeping the humidity lower, especially since its in a closet.
Is that closet closed often or always? I have a similar set up, filtration is behind the wall. however my filter is in a utility room in a pantry like thing and the tank is in its own room.
That hole transfered alot of air, gave the moisture somewhere to go epecially if the doors were closed.
Id paint the closet again with kilz or something of the water proofing like as well as mudding the opening so you can get some protection on the actual drywall itself.
You dont want to put a dehumidifier in there(nor a humidifier since you are dealing with excess moisture as it is) the dehumidifier would help the sump's evaporation more.
I used a piece of plexi and some of that CLEAR plastic corner protector stuff, GE1 silicone and made my sump a lid. I did leave a few inches OPEN where the sponge is at due to the shape of the sump being on an angle to go to the inlet portion of the sump. My uncovered sump behind my 52 evaporates almost 2-3x quicker then the one with the semi cover on it. I dont drop Ph because I use Co2
to control that, the only thing I notice is my Kh
drops but I dont think evap has anything to do with that since I use acid and alk
buffers plus equilibrium.
If you dont want it to look like crap, check those laundry hook up housings, they are plastic and come with a trim ring as well as deep enough for the wall to stop moisture from getting inside the wall itself. Seal with any caulking as it doesnt come in contact with the water.
Something like this
Washer Outlet Box: Mobile Home Parts Store
you can cut the backing out of it and have a thru wall or get two and back to back them so both sides are finished looking.