feeder goldfish are not good for your garter
you can read about it in more detail here:
http://www.thamnophis.com/caresheets...?title=Thiamin,
most people try to switch their garters to something else as soon as possible
feeder minnows, or rosy red feeders, are a good fish alternative, but they don't grow very big and they also contain thiaminase - just a less
trout and salmon strips are a good alternative