Ok, let's see if I got this right. What you are worried may be aiptasia are small feather dusters. Keep that s.g. between 1.023 and 1.026 and these will spread and keep the water column clean. Odds are you have tube worms in there too. Also good.
The one you ask if it is a coral is a bit hard to make out as the photo is lacking in perspective. Can't make out the relative size. I am 90% sure it is a sponge of some sort, so same advice as with the tubeworms/feather dusters. There is the odd chance it is some sort of bubble algae, which is bad but easily controlled with the aide of a mythix crab (emerald crab) which is good to have anyway.
Rats there was a third one there I can't remember now.