3 or 4 green chromis in a 40g?

[michika]

They're cute little guys. They'll school if they have the oppertunity and the space. I have a pair of blue and a pair of yellow and they school together. I know Ed_Holland also has about five or six blue and they school beautifully.

I do believe it is the space and current that will dictate if they school or not. 3 or 4 chromis may school. You do also have to make sure when your choosing your fish that your not picking the loner hanging out in the back, as that may also be a reason why they don't school in smaller tanks.