Thought I would throw my 10 cents worth in here. I put a 10g inside of my 220g, for several purposes; it is the intake diffuser for my sump, water flows over the top through a homemade grill down through gravel into an UG filter then up the lift tubes into the siphon. It is my baby tank. And lastly, slowly turning it into a refrugium by adding plants and mosses. Sorry, pix won't help as I have the plumbing hidden behind slate/moss. The whole thing including sump is a bit complicated but works fantastic.