arr.....Yes, I know metal halide needs ballast. But I want to know if i need to use a RemoteBallast or I can use the common ballast that will attached next to the light bulb. Thanks
remote ballast is the box with coil and capacitor; the energy source for the light bulb. It called remote ballast, because it can seperated with the light bulb with the power cord. by doing that you can have your light bulb hang on the tang and the ballast on the ground. That way, it can reduce the heat by having them together, because both light bulb and ballast will generate significant of heat.
As long as your MH is about 10 or 12 inch away from the surface of the water it won't generate too much of a heat. You can use any ballast you want as long it is setup to run that MH bulb.