Hallowhead
NJRC Member
Most crabs are bad actors, or end up being so when they get larger. You may be fine, time will tell. A perfect example would be emerald crabs. They're perfect reef inhabitants for many people. When you see a thread asking if they're reef friendly on R2R, you'll have a ton of "yes they're model reef citizens" responses and some talking about how they terrorized their reef. If they're well fed, you may never have an issue.
If you want crabs in there and have confidence that you won't have an issue, you can try porcelain or anemone crabs which are filter feeders.
Good luck either way!
Dave
Understood I will keep an eye