I have a 6ft x 15in x 18tank. I have a 7 inch Jack Dempsey cichlid and a 7.5 inch red tail catfish. Everybody is saying that my fish are going to become stressed in the near future because the tank is too small. Now i realize that my catfish will eventually outgrow the tank, but from now until even the one foot mark I don't understand why it would make an impact. Especially since the fish have never in their lives experienced a bigger tank. How do they know what theyre missing? I mean 6ft is a pretty good amount of swim space and they can easily turn around in the tank. I want to keep my fish as long as possible but I have a plan set in stone for when my catfish outgrows the tank. I honestly don't see my Dempsey ever getting too big for my tank. Thanks for the help! and I am looking for solid, backed up answers not a "just because" type answer.