If you just have one left..it's okay...it'll split in a matter of weeks, days sometimes. Wonderful little "flower" from the sea that's hardy, easily taken care of, and helping getting rid of uneated food.
..i never gave them anything and they seem to split anyways, growing. Feed them if you like but i don't think they really need to be fed. If you have fish, they'll take the leftovers i guess...they're filter feeders.