I am stocking a 75 gal 48 long all my fish are juvies and I am having trouble imagining how much room they will need full grown. I have 1 koi angel, 1 electric blue acara, 2 boesemani rainbows, 1 red rainbow, 1 blue rainbow, 1 rainbow I cannot identify, and a dwarf maccullochi rainbow. I added lots of caves and plants for hiding and everyone is doing well- I would really really love to add a severum- will he be too crowded