As an aside, your tank, sorry to say, is definitely not suitable for the yellow tang for any period of time. In a 30 g tank, realistically, you are looking at 4-5 small fish. Tangs are very active and need a lot of room. It really is not suitable, I hope you will reconsider or at least research that purchase a lot.
It is really important to know your water parameters. Again, what is "perfect" for fish can be fatal for these stars. Keep in mind the chocolate chip may/will eat snails, any corals, anemones, etc that you may put in the tank over time. Most other seastars, except for brittlestars, would not be suitable for this tank size as they can not be spot fed and rely on 100+lbs or more of live rock.