My green terror bit one of my goldfish eyes off I’m experienced with both fish but I’m not sure how to medicate him
Firstly, experience asks why you even had a green terror and a goldfish together. a cold water fish and warm water fish? Also what size aquarium are they kept in. As for medication, put in some indian almond leaves which are antifungals. Then, just watch your fish for symptons. If something pops up, probably fungal or bacterial, use a medication from the marcyrn line. Everything from that line is very effective.
edit: i'm going to add that you need to separate the fish if it wasn't said clearly enough already. You can't keep them together. green terrors are too aggressive.
You shouldn’t have a cichlid with goldfish. Their temp requirements aren’t even the same. Goldfish like cool water and cichlids warm. Green terrors are very aggressive I suggest you rehome one of them. The goldfish will eventually be killed.