Brightwell Aquatics LUGOL"S is an extremely powerful iodine solution. It should only be used by advanced reef aquarists to dose iodine. The importance of iodine in a reef aquarium cannot be overstated. Presence of iodine is vital to hermatypic invertebrates (i. e. , corals, clams, and their allies that harbor zooxanthellae) because it is used to detoxify excess oxygen produced by zooxanthellae. This oxygen irritates sensitive tissue. Corals and clams that appear to shrivel or close under intense lighting are attempting to shade their zooxanthellae crop to reduce the rate of oxygen production. Iodine (as the iodide ion) essentially bonds with oxygen to form non-toxic iodate, relieving the need to shield zooxanthellae and enabling the host organism to open fully. Liquid.