I have a 20 gallon high with 3 peppered corydoras and 1 koi angelfish. The tank has been cycled for about three months with the corys in it and I added the angelfish a couple weeks ago. I was wondering if I could add more fish like bosemani rainbows(if so how many) and that would complete the tank, or if the tank is already full. Water parameters are all perfect and tank is crystal clear.