For me, 4 bulbs is not enough. I just did a frag tank & agonized about lighting. I tried 2 other sizes. My frag tank dimensions are 36x18x12. I got the ATI 24" 6 bulb fixture. It's perfect. Good luck... Ron
I also have a 48" 4 bulb ATI fixture I got off here from beanmachine that I don't think I will be using. Let me know if you're interested in either, I need to pick-up my contacts this week anyways.