Broken Fin

Question
My fish is around two/three inches, I dont know what type of fish he is but he is black and quite chunky in  a way. We have five fish including him, we dont have a fliter, we change the water every week or less sometimes; the tank holds around 10-20 litres i think, it's quite a big tank. My fish has broken a fin, so we think. He keeps going around in circles, floating to the top and rolling over. His fin became caught in our filter/pump and that's what we think has caused his fin to break. I think he's going to die soon if we can't mend his fin. Do you know what we can do to save my fish?

Answer
Hi Charlotte;

His fin isn't the problem I'm afraid. The tank is just too small for him. Change his water every day until you can get him a bigger tank.

Your fish sounds like a fancy type of black goldfish. All goldfish need lots of space and good filtration to help control their wastes. He needs at least 40 liters of water to be healthy. Here is a good web page about goldfish and what they need;

http://www.firsttankguide.net/goldfish.php

At Your Service;
Chris Robbins