I agree with the others.
The minimum stocking for fancy goldfish is 20 gallons for the first fish and then 10 gallons for each additional fish. So for the 3 fish you have you would need a
minimum of 40 gallons. If you are un able to do this, then you will have to re-home the fish or take them back to the store.
The reason for this is because goldfish give off a lot of waste through their gills whilst breathing and from their own waste. If they are kept in too small a tank, or the tank is overstocked, or the filtration and maintenance of the tank is poor, the fish will become extremely ill and will quite possibly die.
That may sound a little over the top but honestly, I once had 2 goldfish in 5 gallons and lost one within a week. (The remaining goldfish now lives in a 3 foot, 23 gallon tank and is doing much better) but I would hate to see the same thing happen to you Harley.
A 40 gallon tank as a minimum with filtration that's 10x the tank size (so in this case 400 gallons per hour), would sort things out in this situation. The reason the filtration needs to be so high is because of the amount of waste given off that I mentioned above.
Please if you have any more questions, do not hesitate to ask us. We are here to help
Author