Small white spoys on my new goldfish

I bought a 30 litre tank and filled it with tapwater. I added the mixture ( to get rid of the chlorine etc etc ) I also washed the gravel and added the ornaments. I added the filter and switched it on. I then waited a week and added one goldfish ( about an inch and a half long ).

He has been bobbing around and full of energy and seemed quite ok, from what I can tell. The I noticed small white spots on his fins about the size of a pinhead. I have googled this and come to the conclusion it is white spot and it is caused by stress. If this is true what can I do about it serious. I've grown fond of my fish and don't want him to die or be in pain.