Well, silver rosy reds would be fathead minnows (Pimephales promelas), of which rosy reds are a mutant strain. But a lot of minnows look pretty similar to that. If you get a chance, please put up a photo.
If they only get 4" long, I'm sure they will be fine. I was just asking because some common minnows, such as golden shiners (Notemigonus crysoleucas), get as big as comets do and could overcrowd your pond.