Shrimp will be gone lickity split, I have a pinktail in a 210 fowlr, that 125 is way too small, he will out grow it eventually but I would never put him in a reef. Mine is about 5" now, he picks up rocks and occasionally crunches up a hermit in the shell and a snail. He even grabs my toothbrush when I'm cleaning. The thing about triggers are they just go a bit nuts from time to time, if he went on a rant he could do some major damage, crunching up corals and moving things around. In the 700 he might have been quite different, but for how long?, he will be much different in a smaller tank.