If you intend only to keep fish and inverts that do not require much light, you can probably use the fixtures you have. I'm guessing they are 48" instead of 36"? 36" lamps are 30w. Four 40w bulbs should be OK for a FOWLR
and will give you coraline growth as long as you keep calcium/alk
levels up. I have had good results using a combination of PowerGlo and MarineGlo bulbs in an even mix. Another, and probably the best solution, is to get URI bulbs. I'd go with 2 White and 2 Actinic bulbs there. If you wanted to keep some soft corals, mushrooms, and other inverts with fairly low lighting requirements, you could upgrade to a VHO
system. Four 48" or 46.5" VHO
tubes would give you 440 watts as opposed to 160 watts with the other system. For stony corals, anemones, and other high light critters, you'll need MH
lighting...possibly with actinic supplementation depending on what color temp your MH
bulbs are. You really need to determine what your goals are for the tank...that way you don't have to spend money twice on the lighting. There is also T-5 fluorescent lighting available. I can give you a contact for T-5 fixtures that are built on a custom basis if you want. PM me if you want the email for that. If you can give us an idea of where you want to go with the tank, we can make more specific recommendations. Welcome to AA.com!