well to tell u the truth find a big one right away... I have my motoro, 6" in a 55 right now while i am building my 300 gallon.... but just make sure you follow through with getting it.... The only reason I got mine and put it in my 55 was because the lfs was holding it for me and my tank got delayed from getting here... but i figured to put him in a 55 for 2 weeks while the tank gets running would be fine