Reef Iodide is a concentrated (8000 mg/L) source of stabilized potassium iodide for reef aquariums that restores and maintains iodide levels consistent with those found in the natural environment. It is formulated to provide a safe source of iodide that will not convert to toxic free iodine. Iodine is as toxic as chlorine and should never be used in a reef aquarium. However, iodide is as safe as chloride. 500 ml treats 40000 l.