Ok so the other day my mum decided she would buy me a new addition to my fish tank. Without knowing what breed it was or doing any research before hand she went and baught a fish from our local pet store.
She came home with a clown loach which I called loachy and was very interested in its behaviour so i looked them up. I noticed that my fish tank wasnt very suitable for loachy and now im sort of worried.

: my fish tank is fresh water (no heating) with a blackmoore goldfish, two smaller goldfishes and now of course loachy. There is one filter that moves the water around, a 'fake' plant and an empty headed skull (loachys favorite place)
the tank is only about 20 by 30 centimetres in length, not nearly big enough for 'clown loaches' from what i read.
I tried to tell my mum that my fish tank was unsuitable and loachy could easily die but she refuses to believe me and says he will be fine in the tank and wont 'grow very big'

what should i do? I dont want him dying on me! I really like him as a fish but i want him to be happy. how can i convinnce my mum?
what should i know about clown loaches?