I just returned two Chinese algae eaters because they were killing my other fish. Even when they were young (when I first got them), I did observe them chasing each other around the tank, and the larger one would chase the smaller one usually. The smaller one would hide in plants or in corners away from the large one.
In terms of why it is thin, I can't answer that....not enough experience with fish. I did feed them algae tabs though once they cleaned up the tank. I took a suggestion from someone on here and got some otos and started feeding then zucchini (started today), and am curious to see if they will go for it.