Hi Carolyn, and welcome to the forum.

I think it might be a good idea if you change his diet straight away. Goldfish are toxic and can make your snake ill, or even kill it over a period of time. Have a read through this-
http://www.thamnophis.com/caresheets...C_.26_GOLDFISH
Your snake needs a more varied diet, ideally you should use 'safe' fish (trout or salmon, cut into bite sized portions is very good), nightcrawlers and pinky mice, again cut into managable sizes.