Here is my 75 gallon setup, 10" Red Belly, 8" Caribe, 7 1/2" Red, two 7" red Belly's and a 16" Pleco and no deaths. Yhey actualy shoal very well with each other. I have Aquaclear 5000 powerhead in the tank also, it does 942GPH so that might help, so my answer is 5.