Thank you very much for your advice, Thor! I didn't know that about overfeeding; do you think it would be best to cut down the amount I am feeding them now or would that be likely to confuse them and escalate issues somehow? Sorry for all the questions, I'd be pretty heartbroken if something were to happen to my fish due to my incompetence.
Definitely no sharp objects in the tank, as far as I know! I have some tank gravel at the bottom of the tank though, and three small silk flowers. Other then that the only item in the tank is the filter, which is labelled specific for the 60 gallon tank. I worried at first if maybe the filter was too strong but I'm not sure if that is even a likely / plausible issue. I feel very clueless when it comes to fish, I'm afraid.
That's a good idea about the short separation though; I will get a large bucket and give it a try tomorrow (too late tonight, I wouldn't want to leave him in there too long!) to see how it goes. Thank you so much for your advice, I really hope I can get this resolved!
