im currently looking to start making my sump/refugium for my 75 marine tank. i wanted to have a section for my heater, a section for my return back to the tank, and inbetween those two sections have a nice deep sand bed with live rock on top. i would ultimately like to make it kind of a separate tank with maybe some corals eventually and have some scavengers(emerald crabs, ghost shrimp, etc) to help keep the refuge clean. has anyone ever made their filter a secondary tank to the main display tank so when someone wants to look at your filter you just have another tank with a couple fish or scavengers in there? i want to have a bunch of live rock in my main tank, but also get some in the sump/refuge. i am willing to do up to a 55 gallon tank for the sump/refuge. are ballasts necessary? and do i absolutely need to drill the tank in order to have an external pump back up to the tank or can i just route pvc out of the tank to the pump?