Depends on how much light you want. I had a 36" Satellite on my 46 g BF and it was no where near enough light so I went with a 4 x T5HO which is a bit of an overkill but I wanted the Aquatic Life fixture because it has the good German reflectors in it. Also wanted the timer unit in it. It also comes with moon LED's though don't care about those. The timer allows me to run 2 x 6 hrs overlapping for 2 hrs with a 2nd 2 x 6 hrs and it provides for great coverage that way. Finally I got it used - like new for a great price $115, just had to change the bulbs from SW to FW.
Have a look at Amazon I believe there is another of these fixtures used for $110 right now.