weedmaese-I kind of get your point about fishes not reaching full potential-for example putting a Dovii in a 240 gallon-a bit crammed for a full sized Dovii but not ridiculously crammed-now try the same with a RTC-maybe your right maybe it wont reach 5 feet but that cat will atleast atleast atleast reach 3 feet-so your philosophy depends on the tank size and what type of fish you are talking about. I too use a 30 gallon for a hospital or grow out tank but for fish under 8 inches-anything larger I use a used 90 gallon.