New to fish 🐟

[Rednekgrl82]

Hello, I have had fish off and on my whole life, but mainly goldfish or guppies. About 6 months ago I inherited fish from my brother when he moved and he decided not to take the fish with them. He gave me 2 glofish tetras, a purple one and an orange one. He had 3 but the purple one killed the pink one which was smaller. He had the 3 in a 10g tank. When I got the remaining 2, I put them in a 20g tank. I really wanted to have more than 2 fish. I started some research and one pet store said that they are schooling fish and that it was stressful to have less than 4 in a school. I waited about 2 months before I bought a new blue glofish tetra. They all have adjusted very well. They seem very happy with each other. And then 2 weeks ago I bought a red glofish tetra. Now my orange one is bullying the purple one. Did I do something wrong or is it normal for one to just change it's behavior so sudden?

[Delapool]

Hi, welcome to the forum

If occasional(?) might just be normal behavior.

[Rednekgrl82]

It just started this week and I noticed yesterday that the tail fin is a little bit messed up on the purple one.

[Cecibella123]

Welcome to the forum. I haven't been here long, but have found some very useful information and advice.
I would ask (beg) that when you consider future fish purchases, you stay away from glowfish. It's a cruel practice altering fish so that they become fluorescent, painful to the fish, and it shortens their lifespan considerably. It may also have something to do with their aggressive behavior, although tetras are often fin nippers. I would increase the size of your school to at least 8-10 fish. I believe that white skirt tetras are the species most often altered into glowfish. If so, they should school with your fish fine. A larger school will help disperse the aggression, so no single fish becomes damaged.