My tank currently has 4 neon tetras, 1 corydora, and 1 betta. My betta is not aggressive at all towards the other fish and actually sticks with the cory when hes not at the too of the tank. I'm thinking of getting more corydora but I'm afraid my tank will be too crowded. What is the proper amount of corys to have in a 10 gal tank? Any other advice based on the fish I have in my tank, as well? Thanks!