Help..... my goldfish

Question
HI Lauren, I have to goldfish one is big and the other is a lot smaller. The smaller one has started getting black stuff on its tail and its tail is looking very small. it isn't a very big tank 30cm long and 15cm wide. Im not sure if that has anything to do with it but the bigger fish seems quite happy. please help me.:)

Answer
Hello, I have changed your question to public so other people can use this question incase it has happened to you.

If it has only just started to go black it basically means its not getting the right amount of nutrients. this happened to me so all i did was feed them tropical foodas tropical food contains more nutrients that goldfish apparently dont need.

Or if your goldfish always had this black ness on the tips of its fin it could still be young, as goldfish are born black or brown so he/she could still be getting its adult colours

Lauren