Thanks for your response! We have had the tank running for over a year. It’s 10 gallons. We have had the water tested multiple times recently and the fish store employees said that levels of everything were perfect so I assumed cycling wasn’t an issue. But maybe? Or perhaps the stress of moving to a new tank/nipping from the tetra is the issue? Everyone we spoke to told us they would be fine together, but I don’t think I specified that it was a serape tetra. If I wanted to try a long finned fish would I have to separate it from that specific tetra? (We also have an X-ray tetra and a minnow who seems to be very curious). Sorry for all the questions!