i have 8 in a 50g breeder, i truelly believe other than making sure your system can handle the bio load, the way your rock work is done makes difference as well as type of fish you have impacts the amount you can have, and if they are getting along. i myself have always had more fish then most would say i should, but my rock work is very open with alot of caves cut through's ect for the fish to swim in and out of, as well as i have never stacked my rock towards the back, it leave's room in front and back for them to swim around giving more space