Just to update: He came into chat last night and the NH3 was discussed; He used Windex to clean the outside of his tank before NH3 shot up, so I have a feeling that's what caused it. He was recommended to perform a 30% water change along with carbon use and if the fish/corals seemed to tolerate it well, which they should have, to perform another. It wouldn't hurt to crosscheck your readings with another/newer test kit.