Was just about to feed my 75 gallon tank when I noticed this injury on Dory (hippo tang). I got her in a quarantine tank and added some Neoplex to it. Not sure of the culprit. Tank mates include a flag fin angel, 2 clowns, royal gramma, mandarin goby, 3 clown gobies, chocolate chip starfish, 3 emerald crabs, cleaner shrimp, fire shrimp and assorted hermits and snails. Any advice is appreciated.