you can certainly only run MH
. The bulb color will make a difference. Bulbs all have a Kalvan rating which tells you what color on the spectrum the bulb will reproduce. A bulb with a rating of 6700K or 10,000K will produce a light that has more yellow/white in it. A bulb with a 14,000K or 20,000K rating will appear to have more blue in it. SInce corals tend to grow a bit faster under 6700K or 10,000K MH
lamps, many people will use actinic (blue spectrum) lighting in the way of CF
fixtures to add more blue to the lite tank. It is just more pleasing on the eye.