If you don't know what coralline algae is,but spent $250 on a torch,then freaked out about a sponge being on a coral... I think you have bigger issues than the sponge lol. Not to be rude,but that is a sign you need to do a little more research on the hobby,hitchhikers,good and bad organisms and where these corals come from. Just saying.
I would hate to see you make an uneducated guess on something and waste money.
I have been in this hobby for almost 12 years,and I have leanred you cannot freak out when something happens.