Ouch. I would have expected more from a vet.
I would only feed goldfish as a once in a while item. There are a ton of reasons for this. I will cut to the chase and give you two important ones. Feeder fish carry a LOT of disease and parasites. Feeder fish are not that great of a nutrient source especially for calcium.
A better source for calcium rich feeders would be crickets feed collard greens and mustard greens. Called gut loading your feeders. I would even sprinkle the greens with calcium powder for a boost.
Earthworm appear to be rich in calcium. Try dusted earthworms.