I had a 18" RBTA for about 3 months in my display tank. It was touching montipora corals and seemed to not bother them, but it relocated to where it was touching acropora, and it was causing them to slowly die over the course of weeks, not overnight like I used to think. Beware, they can move at any time. Mine seemed to like very low flow, as it's happy in my refugium display now.