Do the white spots look like grain of salts?  about the same size too?
If the spots look like white grain of salt or sand , then the goldfish probably has ich or white spot disease.
The first thing you should is do a 50 percent water change to reduce the amount of ich parasites in the water or move the goldfish into a temporary hospital tank and treat it there.
The medication that can be used to kill ich is formalin or malachite green or a combination of the two. A brand that contains these ingredients is called "Quick Cure" . Follow the intructions on the bottle but continue the treatment for 12- 14 days instead of a few days in order to get rid the parasites completely, since these parasites exist in different stages during their life cyle in the water and they are only vulnerable during the larval stage.