my goldfish is sick

Question
I  bought two gold fish(one white and one orange) about a week ago and have them both in a tank with and air pump.  the white has been lying at the bottom of the tank for most of the day, his tail looks to be turing a yellow colour and his top fin is flat.  there is also a balck spot on the top of his head and on his fin.  what can i do to help him?

Answer
Hi Kirsty,

This is often the behaviour of new goldfish when they are introduced into a new tank.  If you are very worried, take out all but 6 inches of water and see if his fin is still down.  If it is, put the same water back in and send me a follow up question.  If it isn't, put half of the water back in.

I hope I helped,
James