I have one in my 60 gallon hex reef. It will kill your mandarin, then eat it. It did the same to mine. It also killed a firefish goby, coral banded shrimp, a bangaii cardinal, a mono fish, an achilles tang, a powder brown tang, and several others. These fish were not all in the tank at the same time, but he killed all of the above in less than a year. Like 6 months. You do see him though...not that it's worth it...