A few things I'd like to add to the list of these "Chinese Plecos/butterfly loaches". And I'm hoping that I'm talking about the same fish here:
I have two different species:
Gastromyzon Sp (Hillstream Loach or Borneo Suckers)
and Gastromyzon punctulatus (Spotted Hillstream Loach).
1) G. punctulatus is not territorial and very peaceful. G. Sp is extremely territorial, and kicks the butt of any other Hillstream Loach in it's path including poor little punctulatus.
2) G. Sp will eat anything he can stuff in his mouth - namely catfish pellets - is possessive over it's food, terrorises poor little corys and 'flys' at the tetras and even the Angelfish to get them away. G. punctulatus mainly eats aufwuchs but doesn't mind a bit of fish food here and there and is generally very quiet.
3) I kept both these species in a fast flowing tank with Barbs. I had the temperature at 24oC and they were very active and healthy. When I put them in their own tank and turned the heat down to 22oC they became less active, less boisterous and not as colourful. They stopped coming out for food as often and looked thoroughly miserable. I'm going to persevere and see if there are future improvements.
I'm not convinced that you can keep these fish like you keep goldfish. I think that they require special conditions - fast flowing, well oxygenated water at a temperature of around 22 - 23oC. Not an easy temperature to keep up in my house without a heater.
I feel so sorry for those fish sold as "Chinese Plecos", as they're nothing like a Plec and have very different needs.