Seachem Reef Iodide™ is a concentrated (8,000 mg/L) stabilized potassium iodide source for reef aquaria that will restore and maintain iodide levels to those found in natural sea water. It is formulated to provide a safe source of iodide that will not convert to toxic free iodine under storage or reef conditions. Iodine is as toxic as chlorine and should never be used in a reef system. However, iodide is as safe as chloride

Most iodine supplements on the market are simply potassium iodide or a medicinal disinfectant commonly known as Lugol’s Solution. Lugol’s is a highly concentrated iodine/iodide solution that is highly toxic and intended for disinfection. Although such products are sold for use in reef aquaria, we believe the risks vastly outweigh the potential minor benefits

Potassium iodide only products are a safer alternative but not very effective alone owing to the unstable nature of iodide in the aquarium environment. When added to an aquarium environment, iodide becomes unstable converting to elemental iodine (which is biocidal), iodate (which is useless to corals, toxic at elevated levels, and can't be tested for), and iodide which is the only form of iodine available to corals for uptake. These products' inherent instability makes them potentially dangerous to coral health.
Unlike competing products

Reef Iodide™ is complexed to a stabilizing compound in order to keep it in the iodide form when added to the aquarium. All of the product remains usable and fully bio-available