Reef Chemistry Question of the Day #11

Randy Holmes-Farley · Sep 23, 2014

Reef Chemistry Question of the Day #11

Reef aquarists who choose to dose iodine have a wide variety of possible chemical forms to select from.

What are the two most common forms of inorganic iodine in natural seawater, and which one is usually present at higher concentration than the other?

Good luck!

lionfish5740 · Sep 23, 2014

NaI and KI is my guess

marke · Sep 23, 2014

Potassium iodine is very common! When you answer this question can we discuss the following. If we use potassium iodine does it also increase potassium levels? Is iodine really needed or depleted and should we test? Which test kit do we like? Is iodine or iodide a better addative ? Can it be toxic if too high?

leptang · Sep 23, 2014

iodate IO3- and iodide I-
I dont dose it but its probably in seaweed i feed my tang

melev · Sep 23, 2014

I just wanted to stop in and say Hi Randy!

Randy Holmes-Farley · Sep 23, 2014

Thanks, Marc. It's good to be here.

No answer on the Question of the day?

cheezybuda · Sep 23, 2014

Iodate and iodide. In typical ocean water iodate will be substantially higher. Absolute iodide will vary depending on depth among other factors.

melev · Sep 23, 2014

Randy Holmes-Farley said:
Thanks, Marc. It's good to be here.

No answer on the Question of the day?

I thought we get to ask YOU a question of the day. You're the wizard, after all. :clap2:

Randy Holmes-Farley · Sep 24, 2014

We have two winners today, leptang and cheezybuda!

The answer is iodate (IO₃^-) and iodide (I^-) with iodate predominating.

The counterions, such as sodium and potassum, are moving around independently of these ions, so they wouldn't really be considered part of it.

Here's a blurb from one of my articles:

Iodine in the Ocean
Iodine in the ocean takes a wide variety of forms, both organic and inorganic, and the iodine cycles between these various compounds are very complex and are still an active area of research. The nature of inorganic iodine in the oceans has been generally known for decades. The two predominate forms are iodate (IO3-, with the central iodine and three attached oxygen atoms; Figure 1) and iodide (I-). As a curiosity, note the huge size of the iodine atom compared to the oxygen atoms in iodate in Figure 1. Together these two iodine species usually add up to about 0.06 ppm total iodine (~0.5 mM), but the reported values vary over about a factor of 2. In surface seawater, iodate usually is the dominant form with typical iodate values in the 0.04 to 0.06 ppm iodine (0.3 â€“ 0.5 mM). Likewise, iodide is usually present at lower concentrations, typically 0.01 to 0.02 ppm iodine (0.07 â€“ 0.18 mM).

Organic forms of iodine are any in which the iodine atom is covalently attached to a carbon atom, such as methyl iodide, CH3I. The concentrations of the organic forms (of which there are many different molecules) are only now becoming recognized by oceanographers. In some coastal areas, organic forms can comprise up to 40% of the total iodine, and many previous reports of organoiodine compounds being negligible may be incorrect. Later in this article, some of the organoiodine species found in the ocean are discussed in the context of those organisms that produce them.

All of these various forms can be interconverted in the oceans. Phytoplankton, for example, take up iodate and convert it into iodide, which is mostly, but not completely, released. One research group has suggested that iodate, looking chemically like nitrate, is taken up by the same pathways, and is internally converted to iodide before being released. This process is fast enough that in one local studied, the phytoplankton can convert all of the iodate present to iodide in a month. Iodate is also converted to iodide by bacteria in low oxygen environments of the oceans.

Marine algae can also take up iodide directly, and apparently do so preferentially over iodate. This process may, in fact, be a primary way that iodide is depleted from aquaria, but thatâ€™s getting ahead of things.

There are also abiotic (nonbiological) transformations taking place in the oceans, with iodide being potentially oxidized to iodate. These abiotic processes are probably not the controlling factors of iodine speciation in the oceans, however, with biological processes predominating. In marine aquaria that employ strong oxidants such as ozone, or possibly even UV sterilizers that can promote oxidation, these abiotic factors may predominate.

leptang · Sep 24, 2014

At least i got one right! I use natural ocean water that is filtered by Scripps Institution of Oceanography, its free saltwater and i dont bother testing the trace elements as i do water changes every other week. I am just questioning the amount of iodide there might be in the phytoplankton rich southern California waters? I probably dont need to worry about it. Just trying to learn as much as i can about reef keeping.

Randy Holmes-Farley · Sep 25, 2014

leptang said:
At least i got one right! I use natural ocean water that is filtered by Scripps Institution of Oceanography, its free saltwater and i dont bother testing the trace elements as i do water changes every other week. I am just questioning the amount of iodide there might be in the phytoplankton rich southern California waters? I probably dont need to worry about it. Just trying to learn as much as i can about reef keeping.

Congratulations!

Does Scripps filter that water at all?

In any case, many people (myself included) do not add supplemental iodine. I added it for many years, then stopped and saw no difference. Quite a few reefers have had that experience, although there are still folks who think iodine is useful for them. I'd view iodine dosing as an experiment on any given tank, not as a demonstrated need.

leptang · Sep 25, 2014

Randy Holmes-Farley said:
Congratulations!

Does Scripps filter that water at all?

In any case, many people (myself included) do not add supplemental iodine. I added it for many years, then stopped and saw no difference. Quite a few reefers have had that experience, although there are still folks who think iodine is useful for them. I'd view iodine dosing as an experiment on any given tank, not as a demonstrated need.

Thank you Randy
For what i understand the water has 3 large sand filter you can see it on google map. 8648 Kennel Way, La Jolla, CA 92037 i know the water is used for Birch Aquarium also with a continuous flow. I test the density of the water with my hydrometer and get a salinity of 33 @25c so i add a little salt mix to get it to 35 salinity. The alkalinity is around 6 dKH i boost that up to 7. Ca is 420, I haven't had any real huge problems.

leptang · Sep 25, 2014

And im dosing limewater between water changes and my balance holds.

DRThompson · Sep 25, 2014

Iodide (I) and Iodate (IO3)

Randy Holmes-Farley · Sep 25, 2014

leptang said:
Thank you Randy
For what i understand the water has 3 large sand filter you can see it on google map. 8648 Kennel Way, La Jolla, CA 92037 i know the water is used for Birch Aquarium also with a continuous flow. I test the density of the water with my hydrometer and get a salinity of 33 @25c so i add a little salt mix to get it to 35 salinity. The alkalinity is around 6 dKH i boost that up to 7. Ca is 420, I haven't had any real huge problems.

The reason I ask is that the sand filters probably remove a lot of plankton.