That’s good to hear & yes you cannot go wrong with niacin.Great news about your "wrong end" ducklings. I've never had one pip at the wrong end. Did you have to assist? I went to Tractor Supply this morning and got some niacin for both ducks. I figured it can't hurt. If the weaker one has a niacin deficiency, this should help. I allowed both of them some free roaming time in the house this morning. Older one kept going after the younger ones feet and still pecking. I'm sure they'll grow out of it, eventually. Still keeping them mostly separated for the time being unless under direct supervison.
I did end up having to assist after waiting Almost 48 hours. Sometimes they can do it themselves & other times they can’t zip all the way & have trouble pushing themselves out.