i have a 90 gallon oceanic corner tank.it has a 20 gallon oceanic sump.the sump only has 2 compartmenets.one for the eheim in sump pump and the other has the skimmer.it does have one of the black plastic boxes that is in one side that has three solid sides and one side is egg crate type material.it has a glass lid with a hole for the overflow.i would assume its for bio balls or some other filter media.i was wondering if it would be benificial or worth the money and trouble to put some live rock rubble and chaeto in there.would add a light of course.any input would be greatly appreciated.