what if i add flame angel instead bi-color angel ?

No angefish is ever safe, your always taking a chance especially with any LPS and zoa. SPS are usually safer being as tho they dont have large fleshy bodys or tasty slime on them.
I attribute my sucess to the fact that all my angels were very small when I got them so they never aquired that taste in nature or learned it from others.
But on the same note even tho theyre being perfectly behaved now doesnt mean they might decide they wanna eat them tomorrow
Either take the chance and risk your corals or stay away from angelfish

I have a flame, halfblack and bicolor in a 200g. They all get along pretty well and have lots of space. I have zooanthids, mushrooms and Lps and after about 6 months I have yet to see them nip at the corals. The halfblack nipped the clams to death however :( Im pretty sure clam mantle mucus is like crack to dwarf angels!

Anyway I agree a bicolor is too large for a 30g. Like everyone is saying your always taking a chance with any dwarf angel in a reef. You can try a flame just make sure to keep it well fed. Give it nori seaweed tied to a piece of live rock to munch on instead of your corals. And definately the smaller the better. What about the cherub angel that some people have mentioned?