I know of tanks that have 45 or so in them (tanks are in the 300 gallon range). The theory is that if you spread the hate out, they do okay. I've heard from a reliable source that they have been running for two years without much incident. I wouldn't try it, though. A pair is all you want to try to house in a small tank. I know people who have had three or four (usually of different species) that do okay for a year or so, then start fighting. Maroons and cinnamons are so aggressive that they will shred anything in their tank (including you). They pound little submissive maroons and cinnamons (resp.) relentlessly, IME, when trying to pair them up. I've got a pair of occelaris that attack me every time I put my hands in the tank...