My point is that water quality is directly affected by both size of the tank and size of the fish. You grow a severum up in, say, a 29 gallon tank...sure it's going to be just fine while it's small, but the bigger it gets, the more waste it puts out and the more quickly the water quality will go to hell...therefore stunting the fish. These are, typically, the types of large fish that are returned to LFS. They were bought by uneducated <in terms of fishkeeping> people, put in a tank much too small for them and were stunted by being kept in a tank much too small without the number of water changes it would take to keep the water in good condition.