just going to put this out there. That tank is not going to be a good size for a goldfish.
A 15+ is really the best for a single one. more then that if you have more.
Norma;;y 2 gallons per inch is a good rule of thumb with you have more then one

i too the tank to the store and she told me this fish is specificly good for this tank. just one fish and thts all i wanted.

Pet shops unless based for fish will tell you what they need to make a sale.
Sorry but both the basic fliter and size wont be good for it in the long run.
One it gets bigger you really should think of getting another tank.

I have a fish just like this and he's in a 20 gallon long tank

Its not even a normal goldfish its a pop eyed goldfish. The pet store employey happened to be a personal friend who owned one of these for 6 years in a tank this size. If i need to i can upgrade if and when it is needed to a 10 gallon tank. But this fish has more then enough room in his new home. I allready did my research before getting him. Went to 2 different pet stores , one with a very large specialty fish Section. Its appreceated your making sure i know whats needed , but i allready do and pudge is very happy swimming in his new home.

Do you mean Bubble eye? I don't believe pop is a term used for this.
I as well have a Bubble eye. The size he is at now it will be fine but as he gets bigger you will need a bigger tank.
I had to get a bigger one for my bubble eye as well.

BTW this is pop-eye http://www.fishlore.com/aquariummag.....ish-popeye.htm
So I am pretty sure it's Bubble eye ^^;

Also this may help http://thegoldfishtank.com/
It's a great resource for Goldfish in general.
One thing I have also learned, you can't have sharp things in the tank cause they will damage their eyes

Ok so pudge aint a bubble eye either. He is a telescope eye. http://www.networkcpr.com/goldfish/....._goldfish.html so we are both wrong. I call him a pop eye cuz his eyes literally look like there popped out like in cartoons lol. So we were both wrong and learned something.