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Adding Iodine To the Reef Tank

By Eric Edelman

Adding Iodine to your reef tank can be accomplished in several ways. But before we discuss how to add it, it should be noted that there is no 100% agreement over whether or not Iodine should even be added. In the "hobbiest" sector of reefkeeping, Iodine has been found to benefit soft corals, assist in calcification in stony corals, and enable crustaceans to molt properly. Iodine can also be used as a "dip" since it has antiseptic qualities as well. But this is anecdotal evidence, there have been no true scientific studies to verify the necessity or lack of necessity for adding iodine. Unfortunately, reefkeeping does not have a body of peer reviewed literature available, much of our information comes from hobbiests and product manufacturers.

There are several ways to add Iodine:

  • A commercially prepared Iodine Supplement (Coralife, Kent, Thiel, Wilkens, etc....)
  • Lugol's solution
  • Potassium Iodide
  • Sodium Iodide
  • Tincture of Iodine

Some facts about Iodine:

  • Iodine is a member of the halogen family of compounds, which also include Chlorine and Bromine.
  • Iodine is commonly found as I2. As a liquid it is a dull grey color, as a gas it's a brown/purple.
  • Bioavailable Iodine (the iodine that is considered useful to your reef critters) is generally considered to be the Iodide Ion I-.
  • Iodine is only slightly soluble in water, but dissolves well in solvents such as alcohol.
  • Iodine is considered to be reactive and thus should be dosed on a daily basis rather than weekly.
  • Due to it's chemical properties, iodine makes a good antiseptic and may also be used as a "dip" to cleanse wounds in coral tissues and eliminate certain disease.

Types of Iodine you can use:

Commercially available Iodine supplements generally use Potassium Iodide and several of them use a chelating compound such as EDTA. A buildup of EDTA may be harmful to your reef, the jury is still out on this one, but many hobbyiests try and stay away from chelated compounds.

Lugol's solution is made up of 5% KI and 10% I2 by mass, in water. Many people have switched from commercial iodine preparations to Lugol's solution for economic reasons. A bottle of a commercial preparation may last you six months and cost $10. A pint bottle of Lugol's costs approximately $15 and will supply you with iodine for the rest of your life. Lugol's solution may contain a few problems, as I will discuss below.

Potassium Iodide (KI) and Sodium Iodide (NaI) can be considered together. Generally, a 5-10% solution of one of these is prepared and dosed into the tank. These solutions will dissociate into the positive ion K+ or Na+ and the Iodide Ion I-.

Tincture of Iodine is I2, alcohol, and water. The alcohol is used to keep the iodine dissolved into solution. Tincture of iodine is the least desirable method of adding iodine to your tank, it is acceptable for use as an iodine "dip".

What Happens to Iodine In The Reef Tank

Again, I'd like to mention that the Iodide Ion (I-) is considered to be the most bioavailable of the forms of iodine. Dr. Marlin Atkinson presented his findings at WMC and indicated that KI was a more beneficial method of iodine addition compared to the Lugol's solution due to the I2 concentration in the Lugol's.

In regards to the I2 issue, I2 will break down into I- and IO3- with several intermediates that aren't important since they're short lived. The iodate ion (IO3-) is of concern. This is the little guy that can accumulate in your system, not the I2. There is an enzyme that can convert the IO3- into I- which cures the problem. HOWEVER, the enzyme is called nitrate reductase and in many hobbyists tanks is overburdened with nitrates, and thus cannot accoplish the IO3- ===>> I- conversion. This enzyme is found in photosynthetic organisms. The Iodide ion (I-) is considered to be bioavailable where the Iodate ion (IO3-) is not.

Anoxic areas within your tank (inside rock, under the sand bed, under a plenum) can provide a mechanism to convert the Iodate to the Iodide ion in theory, but whether this actually happens is anyone's guess at this point. So it is entirely possible that some hobbyists who are using Lugol's with good results may have the facility in place to accomplish this conversion. Others may not, which leads to an Iodate buildup in the system.

The iodide ion then is the desirable form of iodine, and it's what we want to put into our tanks. Iodide ions are considered to be necessary for calcification in stony corals, general health of soft corals, and molting in crustaceans.

How Much Iodine to Use

You should look to have an Iodine concentration of 0.02 - 0.04 ppm of Iodine in your tank. Commercial test kits as of this writing are available from Salifert and Seachem.

It is generally recommended that dilute solutions of KI or NaI be used, 5-10% solutions are acceptable here. Commercial iodine preparations do not need to be diluted, they are very dilute anyways. Lugol's solution can be diluted by simply using 1/4 Lugol's and 3/4 water (by volume). Diluting these solutions will prevent overdosing. Overdosing Iodine can have serious consequences on your tank, as it is both a strong oxidant as well as bacteriocidal. In other words, if you add too much iodine, you can wipe out your tank.

Conclusions

If you believe that iodine is necessary to the health of your corals and crustaceans, then you should be adding it to your reef tank.

That being said, if you're comfortable using chemicals that aren't labelled for "Aquarium Use", Lugol's is available at a pharmacy store (you may need a prescription in some states). Sodium Iodide and Potassium Iodide can be obtained at chemical supply houses. And pet shops and mail order houses will carry the commercially available preparations along with the test kits. The Iodine test kit is pretty much essential if you're going to be adding Iodine to your tank. My recommendation is to stay away from the Tincture of Iodine, it contains alcohol as well as the least amount of bioavailable iodide ions.

Happy ReefKeeping!

Created by liquid
Reefs.org
Last modified 2006-11-24 18:40
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