Sick goldfish, high nitrite, nitrate and ammonia levels

Question
Hi,

I have one goldfish in a 3 gallon aquarium. I went on vacation for 9 days, and my roommates fed the fish. When I got back, there was literally a layer of rotting food covering the bottom of the tank - they fed him way too much.

His fins are clamped, he has a few dark spots on one side and the edges of his fins, although the dark spots don't look too bad, but I'm not sure if it is something or not. He clearly looks distressed and is breathing fast.

I took the ammonia, nitrate and nitrate readings and they were all the worst color on the chart. I changed a gallon of his water.

I think he might look worse after I changed his water than before. I don't know if the change shocked him, even if it was a change in the right direction.

I want to change more of his water, as all the readings are STILL on the worst part of the chart, but I don't know if that will help or hurt him.

What should I do??

Thanks,
Emily

Answer
Emily,
A three gallon tank is not big enough for your goldfish. The absolute minimum size tank for one is 20 gallons, with a filter made for a larger tank. Test your water and do water changes every day until the ammonia and nitrites are at zero. The most water you want to remove at one time is 50%. Anything higher will stress and shock the fish. Make sure your filter is working properly. If a filter is not working right, it cannot do its job. I strongly suggest getting your fish the right size home.