I wish I had that info, but the tank and the sump = 250G plus a surprising amount in the plumbing, call it 200G with the rocks.I had an option to feed the mrc4r off the return maifold. It could also be fed from the drain. I still prefered a dedicated feed pump as it was most consitent that way. I feed at 1.5x system volume. What's you total system volume?