I run a single 600 watt Finnex titanium on a 120 gallon reef.. in the corner overlow.. along with a 200 watt eheim that kicks on if it gets too cold. Finnex are nicer than the BRS heaters, IMO, especially the footprint which is much slimmer/shorter for fitting in tight spaces. The room stays around 68 F in the winter. The Finnex 600 covers most of my heating needs, keeping the system between 78/79, unless the room drops down to 65 or below. I have a third BRS titanium connected to the Apex, that is a last ditch backup, set at 76F.