[fishoholic]

I had one I, as long as your tank is large enough it should be fine with a lookdown and a lionfish. Mine did not like other fish shaped similar to him but was fine with a foxface, lionfish, triggers, and a Toby puffer. My miniatus was 8" and long as the other fish where around 3" or larger and not shaped like him he seemed to get along fine with them. My 6" lunare wrasse and him were added at the same time and they did fight for a few days but got along fine after that, however he did kill a 3" parrotfish. My King angel also sometimes picked on my miniatus and I noticed he mostly stayed out of sight hiding in the back of the tank behind the rock.

Because groupers a very messy eaters they do create a lot of added waste to the tank so make sure you keep up with water changes and have an excellent skimmer to help deal with it.

Edit: I just saw in your sig. that you have a 175g IMO that is way to small for a lookdown and a grouper. My 230g was a bit on the small side for my miniatus grouper and I know people who thought their 400g tank was a bit small for a lookdown. So unless you are planning a large upgrade soon I wouldn't recommend getting one as it will put to much of a strain on your bio load.