Ocean Aquatics sells Joe's Juice for killing aptaisia & it works pretty good. Turn off power heads, turn down filter returns, fill the included syringe with some white stuff (shaken, not stirred)
& have fun watching the stinging Bleeps melt. I then use my turkey baster to clear any stuff off my surrounding corals. Yes, as advertised, it is actually reef safe & I have BTA clones in the same tank.