This is a discussion on need help.. within the Beginner Freshwater Aquarium forums, part of the Freshwater Fish and Aquariums category; -->
Do you have a pump in your sump pulling water through the hose out of the tank? If so, I don't see why the ...
Do you have a pump in your sump pulling water through the hose out of the tank? If so, I don't see why the surface skimmer I showed you wouldn't work. If it's just working as a siphon, I'm not sure how well it will work, but it still would probably be better than letting all of that slime stay there. I think it's worth a shot. You could also try using a spray bar as your output instead of just a hose in order to cause more surface agitation. Installation Set 2 from this link is an example of a spray bar:
I think you should give that surface skimmer (or something similar) a shot. I've read a lot of cases where people with very little surface agitation (usually in heavily planted tanks) had a lot of gunk building up at the surface and bought surface skimmers for canister filters and used them with a lot of success. I think it would work well for you. You might also want to get the spray bar as well, since you've got a heavily stocked mbuna tank. All those fish will use a lot of oxygen, so having a lot of surface agitation certainly wouldn't hurt.