I saw this clam tank advertised that is 24"L X 24"W x 8"D. I am contemplating buying the tank. The tank is 18 gal with a 20 gal sump. It is meant to be a top down viewing tank. I wanted to get a recommendation on lighting for this tank. If MH is the only option, what wattage bulb/color temperature would be the best for a tank like this? I have a small reef currently, but have never tried clams before.