No, I would have to say it is not a good idea. Halogen bulbs are not the same as metal halide bulbs. They are far less efficient and produce WAY much more heat....especially at 500w. They also have a spectrum way on the red end (probably 2500-3500k) which is not good for saltwater/reef tanks. I would pass, they will end up costing much more in the long run with energy costs (for both running the bulbs and trying to keep the tank cool) then purchasing much smaller (wattage) metal halide systems.