I have a 75 gallon (48Lx18Wx21T), I would prefer a 40 gallon breeder, there is one on Craigslist I may buy for a future BP pickup. The 40 gallon breeders are what I consider a perfect size because of the 18" width, and its a nice 36" long. I dont like the 12 inch wide tanks, like the 55 longs, they just dont seem wide enough for anything but fish but thats just a personal prefrence.