Keep in mind the "living/swimming zones" for each species of fish. This can allow you to get closer to your max bioload without stressing the fish. You wouldn't want a tank full of open swimmers. Blennies, gobies, fish that are in an out of rock structure, open swimmers.....then you have to add compatability too. With some research you can figure it out and have a good combo. The way to mess it up is to impulse buy.