Actually there are many ways you can refigure the back of your tank. The bio balls are said to be nitrate traps however poorly kept LR rubble can trap the same thing as the bio balls do. It all comes down to proper tank maintenance IMO. I changed them out but not for long, I decided that nothing in the rear chambers was best. So aside from a sponge and the skimmer there is no biological filtration in the rear of my tank. I let my LR in the DT area be my filter....