I have a sicce pump that just barely fits but it rattles around the inside of the return section. I'm looking for something that can produce enough flow for a total of 50gallon system and fit in the return section of this sump. http://www.eshopps.com/products/filters/refugium/cube/ I had originally bought a quiet one pro 4000 because the dimensions in comparison with the dimensions on the sump specs seemed to match up however it wouldn't fit (was very close). Anyone have any other recommendations? Thanks! I would probably be willing to spend a bit more on something that has variable speeds and a bit more powerful that can be ramped down for reduced noise.