You may have to wait till it grows up and becomes a full grown somthing!
Sun corals grow faster and have smaller heads, Dendros bigger heads and seem to reproduce alot slower.. ball park it at 10-1 in my tank and I feed approx 3 times a week.. sometimes dendros are more easily defined by having defining colors around the mouth and the white pattern on the tentacles is more prominent... but that being said.. guessing is all you can do.. I have 2 different kinds of tube corals in my tank, have 2 smaller colonies that are yellow and black and largest head size is 1/4", I have 2 other colonies that are clearish and red, largest head size is 1/2". Still to this day cant peg down if they are actually dendros and sun corals.
You find it every where when you search, Dendrophyllia - Near impossible to distinguish from Tubastrea w/o microscopic analysis of corallite skeletons.
You get clues but have to play the waiting game and kinda see how it grows as a colony.
