It is designed to fit into the existing sump chamber (having it custom made out of Acrylic). The existing chamber's flow goes under the stock baffle, but a refugium's outflow should always flow over the top of a baffle. So instead of re-engineering my sump and adding a baffle while the tank is live, I am just having an insert built to the inside dimensions of my sump chamber, but an inch shorter (right to left) so that the water will enter the insert from my tank's overflow, fill-up the insert, then flow over the shorter (top to bottom) side. I'll send a pic when it comes in.