is my goldfish unwell

Question
hi darryl, we just recently purchased a fish tank. the tank is 61cm longs and 36cm high. we currently have 3 goldfish in this tank. 2 where purchased from a pet shop and 1 was won at a fair. we have just noticed that the one from the fair is looking very thin, and has a chunk missing from the top off his head. he is still swimming around but doesn't look very happy.we feed them 2 a day and they have plenty of plants to eat and hide in. can u help, are we doing something wrong. many thanks Chris.

Answer
Hey Chris,

Fair fish are typically housed poorly, breed poorly, and prone to several very serious sicknesses. This fish, in particular, sounds like the victim of Hole In The Head Disease. A common issue with cichlids, and often incurable in feeder fish (like the ones you have now). The best thing to do is increase the vitamin supply on hand to your fish by stopping the flake or pellet feeding, and switching to thawed peas cut up so they can eat it. Try to track down some hole in the head medication, and try it. Although it sounds like the tank is over stocked to begin with, these things will help keep them healthy. Also, make sure to test your water regularly and do all you can to keep it healthy as well. Best wishes, and good luck.