I dont think I would have anything but the two dempseys my self. I actually feel like a 75 is to small but I know allot of people who will say its plenty big enough. I currently have a male JD thats 9" in a 6 foot 150 gallon tank with 1 carpintis male also about 9" and 1 jag male thats about 8". The JD rules these guys in the 150 and bullies them. I used to have two more jags in the 150 with them. The one jag I took out is my male that was 9.5" and another 6.5" jag and the JD kept them all in line in that 150. Watching the JD, carpintis and jag in a 150 I feel like the JD should be in the 150 alone cause he has claimed the whole tank and he doesnt even have a female with him. If he had a female I have no doubt they would probably have killed the jag and carpintis by now. My big male jag and the 6.5" jag now live in a 300 gallon tank.