if you want to kill it off, a high pH solution would burn it off instantly. Take baking soda, which is buffered to pH 8.0. Heat it in a pot on your stove, while stirring. Once the powder moves like a liquid and it starts flowing around the pot, it's ready and will reach a pH of 14 in water. mix a small amount in water and simply apply to the corals (including pesky aptasia) and instant kill. I use a syringe for aptasia, but for your purpose, you can spray/bush it on. Don't let the solution touch anything you want to keep.
I believe, without looking it up, sodium bicarbonate is becoming sodium carbonate (releasing H2 as gas or creating sodium hydroxide?) bah my HS chemistry was too long ago.