Garters and ribbons IMHO have almost identical care requirements. Any questions feel free to ask, but I'll quote someone already. Goldfish are noterious to be infested with internal paracites and have a poor protien content. Overall "feeder goldfish are horrible to feed to any animal.
However one BIG thing you should concider, if you haven't purchased it yet, if its
legal to own in the state of California without a permit. Check with your local Game and Wildlife if this is so, cause the last thing you need to worry about is a big ol' fine.
Here, in the state, of Vermont anything that is native, you can not own at all, without a permit issue by the state and garters and ribbbons are high on that list, amough others. The fine is $75 when I checked 6 mos. ago. We cannot even keep the morphs legally now without a permit.
I have a sinking feeling, that your LPS might be selling an illegel animal, which unfortunatly does happan. Is it W.C. or C.H. ??? So check first if you can own such a species without a permit from the state.
Good luck.