Take one of the long tube thingies (scientific term) and apply a small amount of AptasiaX directly on the oral disk of the aptasia itself. The zoas are already stretching away from the stinging aptasia to there's plenty of room. If you do get any on the zoas, just blow them off with a turkey baster after a few minutes. In order to kill one of the zoa polyps, you'd really have to treat it directly. I've tried to kill zoas with AptasiaX and it doesn't work all that well which in this case is a good thing.