I've got Seachem Iodine Coral dip.
It's very powerful, thick, dark solution and a couple ML in a litre is plenty, it disperses like ink into the water.
You're supposed to use saltwater from the tank with it, but that then relies on the iodine alone. When dipping my Zoas that were being munched by zoa eating nudis (and later, zoa eating asterinas!), I used RO instead for double the punch. The Zoas are pretty indestructible when closed up, so they can handle it no problem, the molluscs and echinoderms can't!