Yes there is another section behind the sump and the guy that i bought the tank from used this for saltwater so he had a skimmer and other pieces in there. This was a custom acrylic sump that the guy had made but i hate!!! The design!!! The sump has no room for wet/dry biological filtration. I think i'm going to build my own sump from a glass aquarium. Would a 20 gallon high be to small for the sump? If so i would use a 35 gallon. (by the way im only 14 so understand that these are my first sumps).