Shubunkin

Question
I have had my Shubunkin for about three years. He is about 6" in length.  He has always been healthy even though other fish I have had died. As of yesterday, I noticed "Tank" my Shubunkin, is not eating and he goes to the bottom of the tank. He does swim around but he is not eating the food flakes which is a first. We have a 10 gallon tank, the water is not changed real regularly. On an average maybe every three weeks. We do have a filter and I feed him Omega One protein enhanced goldfish flakes. The temperature of the water is normal. From what I have read on the internet and your website, it seems there may be toxins in the water affecting his health.

Answer
Marlene,
 The first problem is the tank size. You should have your fancy goldfish in a tank no smaller than 20 gallons with a filter that is for a larger tank. You are having a few problems. Because he is in a tank that is too small water changes will have to be done more often. If the fish was in a 20 gallon, you would only have to do 25% water changes every week. Because he is in a 10 gallon, you want to do the water changes every other day. This is help bring down the ammonia and nitrite levels that I am sure are too high. He is most likely suffering from ammonia and/or nitrite poisoning since his water is not changed regularly. I would get a liquid water tester and test his water for ammonia and nitrites every day. If either one is registering higher than zero, you will want to do a water change. Do this daily until both the ammonia and nitrites are at zero. They have to be zero at all times. Another problem, is you are stunting the growth of your fish. His body skeleton will or has already stopped growing, but his internal organs are continuing to grow. This will lead to a very painful death of your fish if you do not put him in the right size tank as soon as possible. What is the exact temperature of the water, and what other fish have been housed with him, and how many?