My 5.5 gallon tank is slightly overcrowded. I have 4 platies, 4 rainbows, a betta and a cory. The fish seem to be doing fine and acting normal. I am kinda concerned about aireation though. i was thinking about getting an air stone to help with oxygen in the tank, but i wasn't sure that it would be a good idea. Can anyone give me an opinion or some advise? I would really appreciate it !