mine range from about and inch and a half to under 3/4 of an inch. I have seen no aggression at all. They get along very nicely with the tetras and when they all school up and swim together, its great. They even accept the 2 SAE's who will school with the group as well. But when I did bring home my first group of 4, one of them had and eye missing. They would not let him in the group and chased him off and picked on him. I had to remove him. I got 5 more 1-2 at a time and not had any problems with those either. So you may want to look over that little one to make sure there is nothing wrong with him. Get 1-2 more and you will probably see no problems. I have also read they can also be a lone fish. My one eyed fish did fine until he passed which I was surprised he lasted as long as he did. They also LOVE frozen brine and blood worms. Good luck. If you haven't already, pick up some Tetra Color flakes. It helps brighten up their stripes and tails.