You d!ck
I'd like to reiterate. The nitrates are at a constant 15ppm (never higher than 20), They have more than enough room to swim and interact, and most of the time only half of the tank is used. The only fish that uses the whole tank is the arowana (who hasn't grown an inch in a year, he was saved from a 150).
I know the knife will *eventually* outgrow the tank, but, he was 16" long and in a 29 gallon tank, so I saved him as well. All of the other fish are done growing (basically). I have room for a pond in my basement, and that will probably be set up in the near future.
Also, the albino channel cat was once again saved from a 20 gal tank, and now lives in a 1700gal indoor pond.