First off the butterfly is to large for a 30g.
The mandarin is a very ferocious Eater of copepod and you'll need at least 100 lbs of lr to support its eating habits or continually stock copepod in a separate tank for them to breed and grow.
I would stay away from these guys Imo with a 30g tank. Just my opinion, hate seeing them die from starvation in every other posts.
They are the most mellow fish I have, no one cares about him or harasses him.
Please do your research, and get rid of the butterfly.