You should not feed freshwater feeder fish to saltwater fish, it is very unhealthy. Instead get them eating meaty food that are not live, go to the grocery store and get cocktail shrimp, squid, fish, clams. Chop them into bite size pieces and feed them that. If they will not eat non-living food, try putting the food on a feeding stick and moving it around like it is live. There are saltwater feeders (damsels, chromis), but that gets very expensive.
Good luck, don't worry you are not the first person to get bad advise from your LFS, but if you read here and ask a lot of questions your tank should be fine.
The other thing you may want to reconsider now or in the future would be your substrate, you will battle with nitrates with crushed coral, it just traps the debris horribly, sandbeds are much better. be sure you have a gravel vaccume and vaccume that CC out frequently