You definitely want to go based on display size since sumps and refugiums don’t contribute to the load and instead reduce the load. The Double Cone 180 can certainly handle a 150 gallon display but what’s more important is your fish load because a Double cone 180 could support a 400 gallon display if the load were light enough or a 90 gallon display with a VERY heavy load. Our size ratings are based on display size and at the low end of the scale, it’s assumed you’d have a heavy fish load. A heavy load by our standards is 1/2” of fish per display gallon. Our skimmers are very conservatively rated so you definitely don’t want to oversize them but again, it all boils down to your fish load.