I am new to this forum and joined specifically for this question. I have kept fish since 2003. However, I have only been keeping community fish and a planted tank for the past few years. Specs: 29 gallon tall, planted tank, about 10 plants short and tall in a bed of plant food substrate mixed with peat moss and sand. A 40 gallon tetra filter. Water chemistry is: nitrates are around 10, no nitrates, the water is hard, the alkalinity is around 180 or a little higher, the pH is around 7.8 or a little less. These parameters stay steady since I established the planted tank. I have 3 Julii or leopard corycats and 3 panda corycats, and 7 Colombian tetras. When I first got the Colombians I only got 4. However, they started picking on one, and I woke up to a half eaten fish still swimming around, and hiding (the tail was gone and then some
). That poor fish died soon after I found it like that. I was horrified and was under the impression that they are peaceful fish in general. I want peaceful fish. Anyway, I read about them, and got more so that we have 7, and rearranged the terrain. That was probably 6 months ago, and things have been better, sort of. One of the biggest ones is a bully and won't school or hang out with the other 6 unless he is super scared. The other six seem to get along and don't fight that I can see. However, they just stay on one side of the tank, hiding and don't swim around unless I am feeding them. And the bully stays on the other side of the tank, also hiding and not swimming around. My corycats are more active and swim around more than the tetras do! A few days ago I woke up to see one the 6 has the top part of the tail fin bitten off. This is a horrible distressing feeling to have the situation happening again. So, I did a 50% water change, moved the plants and decor around, and put the bully in quarantine to see if they other six would behave differently. At first they were super scared I would take them out too. Once they relaxed a little they began to spread out over the whole tank space, two by two. But, they still do not swim around. The bully in quarantine began trying to jump out, so I felt bad and put him back in. He immediately went to the cave where he hid all night. Then, this morning, they were back to their usual formation of the group huddled on the left, and the bully on the right by the corycats. I considered getting more, but I am afraid this is a bully who won't change. And the local fish shop has only two babies and all their tanks are under observation with sickness. So, that isn't a choice right now. My other thought was to find a home for them via craigslist with someone who has a 55 gallon and more diversified tank. I really like these fish, but I don't want them to live a stunted life. Any advice or tips you have about these particular fish and this situation would be greatly appreciated. Thank you so much.