A newbie can easily be someone who has kept fish for awhile if they are filled with mis-information. And still believing that fish "grow" to their environment = newbie to me.
Why not stick some pirahana in the 29 gallon tank. I am sure it will learn to live with those other fish. (that would be sarcasm of course).
A fish can't choose its instincts anymore than it can choose how its genes work.