[Beverly]

Other interesting quotes from RANDY HOLMES-FARLEY's Magnesium in Reef Aquaria http://www.advancedaquarist.com/issues/oct2003/chem.htm

Supplements for Magnesium in Marine Aquaria

...Whatever supplement you choose, I’d suggest targeting the natural seawater concentration: 1285 ppm. For practical purposes, 1250-1350 ppm is fine. I would not suggest raising magnesium by more than 100 ppm per day. If you need to raise it by several hundred ppm, splitting the addition over several days will allow you to better home in on the target concentration, and might possibly allow the aquarium to deal with impurities that may come in with the supplement.

Effect of Magnesium on the Calcium/Alkalinity Balance in Aquaria

...In Captive Seawater Fishes there is an extensive discussion of the impact of magnesium on the calcium/carbonate system, including a set of data that indicates the magnitude of the impact that magnesium can have.25 In this experiment, batches of artificial seawater were made up with varying magnesium and carbonate levels. The scientists then measured how long it took for calcium carbonate to precipitate from each solution. Not surprisingly, the higher the carbonate was raised, the more rapid was the precipitation of calcium carbonate.

More interestingly, the magnesium levels were found to have a very large impact on the rate of precipitation. In batches with no magnesium, and at natural calcium and elevated carbonate levels, calcium carbonate was found to precipitate in minutes. With a natural seawater level of magnesium added to that mix, the precipitation was delayed to 13 to 20 hours. With double the natural magnesium concentration, the precipitation was delayed to 22 to 29 hours.

Even more strikingly, at a lower level of carbonate (closer to that of natural seawater and probably similar to that in many reef aquaria), precipitation was delayed from a few minutes in the absence of magnesium to 750 hours in the presence of natural levels of magnesium. Consequently, magnesium has a big impact on the rate of precipitation of calcium carbonate (a fact that has been confirmed by many researchers).

Conclusions

Magnesium is an important ion for reef aquarists. In addition to its many biological functions, it serves to prevent the excessive precipitation of calcium carbonate from both seawater and aquarium water. Since both calcium and alkalinity are very important to organisms that we keep, making sure that they are not lost to excessive precipitation is an important part of aquarium husbandry.

Quoting Ron Shimek answering someone's question (in bold) from this thread http://www.reefcentral.com/forums/sh...ghlight=iodine
Quotes in red are as they are shown in Mr. Shimek's reply:

(not arguing) then why are they sold and recommended for reefs?

They are sold because, as Ben Franklin once observed, "A fool and his money are soon parted." People will buy a lot of things on the say-so of manufacturers.

First, iodine.

Iodine is a great disinfectant and preservative. In fact, Lugol's solution was developed (in the late 1800s) by Lugol, as way to preserve tissues. It works better than formaldehyde for many tissues. Some very small amounts of iodine are necessary for animals. However, in a single standard feeding of a tank (see my article in the March, 2002 issue of Reefkeeping Magazine, the average hobbyist adds enough iodine to a tank to raise the iodine level from 0 to NSW concentrations. The problem with iodine in tanks is not that it needs to be added, but rather how to remove the excess.

my clams are growing despite my additions of strotium and iodide.

"Despite" is the operative word here.

The following is a long answer, and for that I apologize, but there really is no short answer.

My reasons for considering Strontium a weak toxin are given below. There is no ambiguity for that conclusion. It is supported by several research papers all published in peer-reviewed professional journals. The only reference suggesting that strontium benefits corals is Swart’s 1980 paper, and it is this paper which is cited by Delbeek and Sprung as evidence that corals need strontium. Unfortunately, Delbeek and Sprung must have missed Swart’s 1981 "follow-up" article where he explained that his 1980 conclusions were incorrect and based on incomplete research - the “publish or perish” syndrome strikes again. Delbeek and Sprung have also missed all of the other references on strontium and corals.... Good literature researchers, these guys ain’t...

There is no specific book on the biochemistry or physiology of coral reef animals, and will not likely be, as most physiologists consider them as perfectly normal invertebrates, so why do something specific for them? Probably the most widely used text on the physiology of invertebrate animals is:

Prosser, C. L. 1991. Comparative Animal Physiology, 4th ed.. Environmental and metabolic animal physiology. Wiley-Liss, New York, 578 pp.

There are a lot of papers investigating the concentration of strontium in coral skeletons. Without exception, these papers were looking at the relative amount of strontium as an indicator of temperature. If this could be done, then paleontologists could use the Sr/Ca ratio in fossil corals to determine the temperature of ancient seas. Unfortunately, after a lot research, it has become evident that this ratio is simply too variable to be of much use.

Relatively few papers have looked at Strontium metabolism in corals. Only the one research paper, by Swart, published in 1980 has shown any beneficial attributes of strontium.

Swart’s 1980 study indicated that strontium supplementation enhanced skeletal formation. He added large amounts of several chemicals, including strontium and calcium, to sea water elevating their relative ionic concentrations significantly above those found in normal sea water. When he added enough strontium to raise the strontium concentrations by a factor of 10, from 7 ppm to 77 ppm, he found that this massive addition of strontium caused a significant increase in skeletal growth. Interestingly, he found an identical increase with the addition of calcium.

The results presented in Swart’s 1980 paper indicate that strontium stimulates the formation of coral skeletons. Unfortunately, such a conclusion would be in error. These data were published prematurely, and were from the initial phase of a longer study. In the final results, Swart(1981), noted that increases in three factors: total strontium concentrations, strontium/calcium ratios, and increased calcium concentrations, ALL caused a growth increase. Additionally, there was a concentration level (approximately 100 ppm above the local ”normal” sea water concentrations, or about 520 ppm) above which the increase of calcium ceased to cause an increase in growth.

Here are the references - I suggest you read them.

Swart, P. K. 1980. The effect of seawater chemistry on the growth rates of some scleractinian corals. In: R. Tardent and P. Tardent (Editors). Developmental and Cellular Biology of Coelenterates. Proceedings of the Fourth International Coelenterate Symposium. Interlaken. pp. 203-208.

Swart, P. K. 1981. The strontium, magnesium and sodium composition of recent scleractinian coral skeletons as standards for paleoenvironmental analysis. Palaeogeogrraphy, Paleoclimatololy, Paleoecology. 34:115-136.

These results indicated that there appeared to be an unutilized potential for skeletal formation in natural seawater in the area of his studies. If additional ions of a chemically suitable nature are present, either calcium or strontium, the coral will use them to form the skeleton. .

Swart’s work indicated that either calcium or strontium will cause increases in skeletal growth provided the total of both ions is less than or equal to about 100 ppm above normal, or a total of 520 ppm. It is important to note that in the results from this study, strontium did not stimulate additional skeletal formation, it simply substituted for ”missing” calcium ions. At the time, what was presumed to be necessary was simply an ion of the right size and shape. In effect, strontium was an acceptable substitute for an unrealized calcium potential and simply substituted in to the skeleton in place of the calcium.

That simple explanation, however, has subsequently been shown to be in error (see the last few paragraphs of this post).

An examination of the scientific literature subsequent to Swart’s work shows that there is NO other evidence for any beneficial effects of strontium by itself to the corals.

Swart also stated the skeleton formed in the solutions containing higher than normal concentrations of strontium show decreased calcification (Swart, 1981), which he thought was simply due to the substitution of strontium for calcium. In fact, there is a small, but growing body of evidence that indicates that strontium REDUCES calcification rates in corals (Chalker, 1981; Swart, 1981; Ip and Krishnaveni, 1991; Wright and Marshall, 1991).

Here are those references - again, please read them.

Chalker, B. E. 1981. Skeletogenesis in scleractinian corals: the transport and deposition of strontium and calcium. In: Handbook of Stable Strontium. S.C. Skoryna (Ed.) Plenum Press. New York, pp. 47 63.

Ip, Y. K. and P. Krishnaveni. 1991. Incorporation of strontium (90Sr2+) into the skeleton of the hermatypic coral Galaxea fascicularis. Journal of Experimental Zoology. 258:273-276.

Wright, O. P. and A. T. Marshall. 1991. Calcium transport across the isolated oral epithelium of scleractinian corals. Coral Reefs. 10:37-40.

Wright and Marshall (1991) showed that strontium significantly reduced the transport of calcium ions across coral epithelial tissues. All calcium used by corals for either metabolic processes or for calcification comes from within the animal’s tissues, not directly from the sea water surrounding it. So, it has to pass through the epithelium. Thus a reduction in calcium transport into the animal will directly reduce all of these processes, including calcification. The presence of significant amounts of strontium could significantly inhibit and alter all calcium requiring processes, such as muscle contraction, tissue differentiations, growth, and injury repair) by reducing the calcium uptake from the surrounding waters.

Additional calcification reduction may be due to the substitution of strontium for calcium in the enzymatic pathways necessary for calcification. Strontium (and other doubly charged positive ions such as magnesium, barium and zinc) will occasionally substitute for calcium in the chemical processes that a coral uses for skeletogenesis. The substitution of strontium for calcium by corals, mollusks, and fishes appears accidental (Sadovy and Severin, 1992). However, strontium is not a twin of calcium and reacts somewhat differently than calcium, and may significantly slow down the calcification process. Thus, if the conditions are otherwise good for the corals, the addition of strontium would inhibit calcification. However, the deposition of strontium in the coral skeleton may not be due to simple substitution, see below.

Any strontium found in the coral skeleton is tightly bound into that skeleton. Such binding means that the chemical is not available to be utilized by, or influence the animal. Many invertebrate animals deposit wastes or toxins in crystalline matrices as a way of detoxifying their environment (Kozloff, 1990). It is possible that those corals whose skeletons contain relatively large amounts of strontium are selectively depositing it in the skeletons. This would remove that strontium from the metabolic pathways, as materials that are deposited as crystals are unavailable for biologically mediated reactions. In this way, any deleterious aspects of strontium ions in solution would countered. This type of elimination of “problem chemicals” is fairly common.

(See almost any issue of the journal, Marine Pollution Bulletin, for references to such pathways).

There is also some work indicating that strontium is rapidly and efficiently removed from the coral polyp and deposited into the skeleton (Ip and Krishnaveni 1991). They found that strontium was deposited into the skeleton of the coral Galaxea fascicularis by a pathway that appeared to be different from that used by the coral to deposit calcium. This pathway appeared to function when the calcification pathway was not working. This could indicate that natural selection has favored the development of an additional metabolic pathway to remove strontium from the solutions bathing the coral. Such a pathway would ameliorate any toxic effects due to this chemical, and would facilitate across membrane transport of calcium and subsequent skeletal calcification.

Finally, more recent work, in this article
Greegor, R. B., N. E. Pingitore Jr and F. W. Lytle. 1997. Strontianite in coral skeletal aragonite. Science. 275:1452-1454, shows that strontium is not actually substituting for calcium in coral skeletons, but is actually being deposited as a different and distinct mineral.

The bottom line is this: Coral physiology is adapted to remove strontium from the interanl coral environment and place it into the skeleton (where it is insoluble and therefore harmless). Strontium interferes will all sorts of normal physiological responses (calcium is used for everything from the production of eggs and sperm to the relaxation of muscles - and strontium interferes with these repsonses). Corals have adapted to the strontium concentrations in sea water by developing specialized chemical reactions specifically to remove the strontium from their tissues.

By adding strontium to aquaria, hobbyists are simply adding a burden to their animals that in some cases can be enough to cause deleterious effects.

And they are poisoning their animals on the advice of manufacturers selling the poisons.... Sorta like listening to cigarette manufacturers telling you how good smoking is for you...

Anyhoo, I'm going to keep on testing and adjusting Mg at least every two weeks, trying to keep it at 1300-ish ppm. Am not going to supplement anything else after doing all that reading