Trace Elements

[Robert Jordan]

Craig,
In your article on the Composition of Several Synthetic Seawater Mixes, most of the trace elements are much higher then seawater. The copper concentration seems way too high unless I am not doing the math correctly as Micromoles * Molar mass = ppb. the copper concentration is listed as 1.8 micromoles for Instant Ocean salt . I get 114 ppb as the answer or 0.114 ppm. This I believe is wrong on my part . But if it is correct , then this is near the treatment dose for fish. Obviously, the concentration then must be the total concentration which includes dissolved and undissolved copper. Can you add a bit more info on the trace element testing. I am especially interested in both forms of copper. Thanks, Robert.

 

[randy holmes-farley]

The metal concentrations are much higher than NSW in many salt mixes. Whether that is a concern or not is open to debate, and in fact, has been debated extensively. Ron Shimek, in particular, has published a number of articles where he claims that we are killing corals. That fact has yet to be demonstrated, but the concern is real. The caveat is that nearly all of these metals will be bound by organics in our tanks, reducing the bioavailability in many cases. So the fact that the absolute concentration is elevated does not really demonstrate whether the metals are present in too high of concentrations for optimal biological function, to low, or just about right. Ron is proceeding to test their toxicity in a sea urchin assay of some type.

 

[Robert Jordan]

Randy,
Thank's for replying. I'll hold off on further questions until Ron Shimek submits his assay on the toxicity. I know you will take it into account if you decide to submit an article on copper to "Advanced Aquarist". This should clear up questions on Copper sulfate as we use it at 0.15 ppm to treat fish with and the difference between that and the high concentrations in the salt mixes. As I understand it now, the metals are bound by the organics in the tank and removed by skimming and are bioavailable only under an unknown concentration. I'll be looking forward to "Ron's" assay. In the meantime, Your recommendation to add some iron when growing caulerpa or chaetomorpha algae is right on. I set up a 4 gallon tank to grow caulerpa next to the main tank and fed by a gravity system. So instead of dosing the main tank which requires much more iron, I shut down the gravity system and dose one drop using "Kent Marines" product into the smaller tank and allow the algae to feed on it for two hours after the lights are turned on. A small powerhead is turned on for circulation. The results I see are remarkable. When the lights are turned on, I can see new growth of the caulerpa (smaller grapes) and they are pale. But after two hours most of them have darken up quite a bit. Then I turn on the gravity flow and the concentration is then diluted by the main tank. I feel safe about doing it this way until we learn more about the trace metals. Kent recommends 8 drops per 50 gallons and no more then twice the dose. So I am within the range of their instructions. In the coming weeks, I may decide to increase the dose to 2 to 4 drops and I'll still be under the recommended dose for the whole system. Bob.