lemon juice injected with a syringe has worked for me quite well. I have also tried AptasiaX, it comes out of the syringe as very heavy drops that dont dissipate, drops straight down and kills aptasia really really well. You dont even have to touch the aptasia. when using the lemon juice, I actually stabbed the aptasia so the juice wouldnt go anywhere else. I dont know if just getting the juice near the aptasia will work.

Rey