I have a sargassum in my reef. Didn't bother any existing fish in the system including small chromis and others. A very aggressive eater, but does not attach shrimp, crabs, snails, etc. Doesn't bother corals either. I did add one new fish that my powder blue tang chased and the trigger joined in on the fun, but didn't do any real damage. Definitely more peaceful than the powder blue. Personally, I love the sargassum triggers. It is going to outgrow my tank someday, but it is really a very attractive fish with tons of personality. It even knows the formula 2 food jar when I pick it up besides the tank. He's very curious about anything new that enters the tank. He often bites holes in bags when I'm floating new corals/fish so be careful of that. Also, I put a frag in that had wet super glue on the end and he bit onto that. I had to pull the superglue off his mouth with tongs... He's ok now.