Okay, so basically what happened was I got a new goldfish a couple days ago so my old goldfish wouldn't be all alone. They both live in a 2.5 gallon tank as of right now and I am planning on getting them a 20 gallon within the next month. I'm only 15 so I can't just go out and buy things, If I could I would... But anyway, so I noticed that my older goldfish got a rip in his tail. I looked it up and brushed it off as "he probably just got it caught on something and he will be ok as long as it doesn't rot." But then this morning I noticed my new goldfish bumping and nipping at him. So I suspected that the new goldfish was being mean to him and could've caused his tail injury. Taking this theory into consideration I put my old goldfish in a medium sized plastic tub to seperate the two. After school I got home and noticed that the goldfish seemed to see eachother through the plastic and were trying to swim to eachother as if they missed one another. I decided to kind of "expierement" and put the new goldfish in the tub with the old one and they both seemed fine. Now I put them both back in the tank and they still seem to be ok. The new one isnt bothering the old one. So I'm not sure what to do or why the new one could of been hurting the old one. Despite the fact the older one is a bit bigger.