It is rated to 525 US gallons, it holds 2.6 gallons of media and the reactor is 8" diameter, 20" tall. I think outside of the highest possible demand for a tank your size it should work, and even slightly outside its capacity, a supplement with talk would be all that is needed. Really, I would count your system as 400 gallons as the volume of a sump or refugium is not going to have a calcium demand.