FWIW, I did regular 1% daily water changes and also dosed iron and silicate.
Here's my conclusions from ICP testing that tank and what impact those procedures had on certain trace elements. I include iodine and silicate for interest, but note that those are not trace elements.
Recently, Triton GmbH in Germany has initiated a method of testing many ions at once for a single price. In the US, that service is coordinated by Unique Corals. For $49 they will send you a couple of tubes to collect a tank water sample, and a prepaid mailer to send the sample back to them...
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Molybdenum (Mo). Molybdenum is low, and if that is true, it’s an interesting and potentially important result. I don’t typically add any trace elements. I may consider adding some molybdenum as it is biologically important.
Vanadium (V). Triton can just barely detect the natural level of vanadium (1.8 µg/L) since their LOD is 0.9 µg/L. Still, detecting none suggests it may be depleted, and is another possibility for dosing.
Zinc (Zn). The zinc is about spot on, so there’s not much to say about it.
Manganese (Mn). Triton can just barely detect the natural level of manganese (0.17 µg/L) since their LOD is 0.12 µg/L. Detecting none suggests it may be depleted, and is another possibility for dosing, but I have less confidence that this one is really seriously depleted since it is so close to the LOD. But Mn is biologically important and I will consider it.
Iodine (I). I don’t generally think that dosing iodine is useful for me based on my experience in dosing it for years, then stopping and seeing no difference. Many people have had that same experience. I also know that iodide and iodate deplete in my aquarium based on kit testing I’ve done in the past. So it does not surprise me that it is depleted since I do not supplement. Triton also detects organic forms of iodine, so when some folks (maybe especially those not doing water changes or skimming) get very highly elevated levels of iodine, it may be organic forms they are detecting. That is an interesting area to pursue since this sort of test is the only way to do studies on organic iodine levels.
Iron (Fe). The natural iron level varies a lot with depth, but surface seawater may have only 0.006 µg/L. The Triton LOD = 0.3 µg/L. I dose iron, and when I dose it I boost iron to roughly 1-2 µg/L, which would be detectable. This sample was taken more than a week after the last iron dosing, and none was detected as it gets depleted in the meanwhile. I’ve not yet seen a Triton test result for a real aquarium sample that had detectable iron, but that doesn’t mean these tanks are necessarily deficient. Iron is also a case where the form is critical, and ICP cannot distinguish form. Binding to organic matter, for example, can alter the bioavailability of iron.
Chromium (Cr). Chromium is present in natural seawater at roughly 0.3 µg/L. The Triton LOD = 0.9 µg/L), so having none detected may be fine. We cannot really tell much, unless there is a substantial excess.
Cobalt (Co). Cobalt is present in natural seawater at roughly 0.006 µg/L. The Triton LOD = 0.4 µg/L), so having none detected may be fine. We cannot really tell much, unless there is a substantial excess.
Silicon (Si). I dose silicate (as sodium silicate solution) to my aquarium. I boost the concentration to about 200 µg/L of silicon equivalent once a week or so. This water sample was drawn one week after the last dose of silicate. I know from previous studies that silicate is rapidly depleted in my tank, presumably by sponges (the reason I dose it), by diatoms, and possibly by the GFO that I use to bind phosphate.
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