Cclown, Torch,Hammer and Frogspawn are all corals from the same family Euphyilla. I find them to be very hardy hard corals and good indicators of water quality. They come in single head and branching head forms and come in different colors. They are very forgiven when it comes to light and water current, but all of mine seem to prefer medium light and current. They also like alittle feedings of meaty food once in awhile.
thinhvu, sounds like your brown Torch may have developed an infection. Maybe from being moved, trauma or possibly from water quality or high temperature. Try gently siphoning or brushing away the stuff and make sure that area is getting good current. I lose a branch or two for no apparent reason too, but luckly it doesn't effect the entire colony.
Good Luck
Mike