My least favourite fish has been otocinclus. They're the most sensitive things I've got, and while I've probably done more work for them than for any other fish in an effort to sort them out, I can't quite make them happy. It was a mistake getting them in the first place, mind you, but I didn't quite appreciate how flighty they were, and that they would be terrorized by the raphael catfish, who wasn't going to eat them but she prowls around like she might. I bought a 60L tank and moved the otos. But I didn't appreciate how difficult it was to keep the PH and other parameters stable in a tiny tank. The cherry barbs who shared the tank with the otos seemed fine, but the otos went on hunger strike, sitting at the bottom of the tank, and I lost three. So I bought a 125L tank -- obviously much easier to maintain and more space for everyone -- shifted them into that. Definite improvement, as they eat algae and aren't sitting on the substrate, but they're not as active as other people's otos are reported to be. They spend 95% of their time hanging out on the plants in the back of the tank.
The other regrettable fish I bought was a second Boliviam ram, bought to be a potential mate for my first Bolivian ram. I think it was another male and either way, the first ram wasn't having it and kept it pinned to the back of the tank, and it stopped eating. I rehomed it.
The other regrettable fish I bought was a second Boliviam ram, bought to be a potential mate for my first Bolivian ram. I think it was another male and either way, the first ram wasn't having it and kept it pinned to the back of the tank, and it stopped eating. I rehomed it.