For instance, if dosing iron, and depending on which type you are using, it can the bind with others and turn into copper, that's fascinating, Im assuming this change can severely harm your reef tank and reef chemistry.
That isn't exactly what I meant. What you wrote is the mythical process of alchemy.
What I meant was that the organic material that is binding the iron (the chelator) may come off the iron and attach itself to other metals instead, such as copper.
I discuss the chelation process here:
Organic Compounds in the Reef Aquarium by Randy Holmes-Farley - Reefkeeping.com
from it:
Dissolved organic material may bind to and modulate the solubility, bioavailability, and toxicity of many metals, such as iron and copper. Whether this is good or bad depends entirely on the metal, its concentration, the particular organism involved, and the nature and concentration of the organic matter.
Metals take a variety of different forms in seawater, and these different forms have very different properties. Copper, for example, exists in a multitude of forms.16 In natural seawater it has recently become clear that copper is almost completely bound by organic materials.17 Many of these organics are called chelators. A chelating agent is one that can grab onto the copper from two or more directions at once.
In natural seawater these organics take many forms. Humic and fulvic acids, for example, are two of the most important types of materials that bind copper and other metals in seawater.17-19 They are also known to greatly reduce the toxicity of metals, because in many cases it is the free copper that is the most toxic.17 These classes of organic materials comprise what remains when proteins, carbohydrates, and many other naturally occurring organic materials are biodegraded to a state where further degradation is very slow. Humic and fulvic acids (the distinction between the two being only that humic acids are more hydrophobic than fulvic acids) have a wide range of structures and physical properties. They typically are high molecular weight organic acids, with sizes ranging from 500 to 10,000 daltons (grams/mole). They can also be parts of larger assemblies of organic materials that would be called colloidal (very small particulates) rather than truly "dissolved." They can, of course, be part of particulate organic matter as well if they accumulate into a particle of sufficient size. The humic and fulvic acids are comprised of amino acids, sugars, amino sugars, fatty acids, and other organic functional groups. Different localities and depths in the ocean contain different amounts and specific types of these organic materials. As mentioned above, typical values for the total dissolved organic carbon are on the order of 1 ppm carbon for tropical surface seawater.19 Humic substances typically account for about 10-20 % of that total, and fulvic substances can account for more than 50% in some cases.19
Since trace metals are present in seawater at far below 1 ppm, there may be plenty of organic material to bind most or all of these metals in aquaria. Within these organic materials will be sites where several carboxylic acid, phenolate, thiolate, amino, or other metal-binding groups come together. These sites are where a metal ion will be most strongly bound. Structurally, it is hard to show a "typical" humic acid binding to copper, but the structure in Figure 1 shows one possibility.
Figure 1. A schematic of a copper ion (Cu++; shown in red) being chelated by
a naturally occurring humic acid (shown in green).
In this figure, the central positively-charged copper ion (Cu++) is chelated by the larger humic acid shown in green. It is bound ionically by two negatively charged carboxylic acid groups and complexed by one neutral amino group. Together these three groups may hold the copper ion many orders of magnitude more strongly than could any individual binding group.
The very extensive book, "Biogeochemistry of Marine Dissolved Organic Matter,"19 states:
"The collective findings establish that a significant component of bioactive, or nutrient, metals (Mn, Fe, Co, Ni, Cu, Zn, Cd) occur in the colloidal phase along with numerous other trace metals."
What does this mean for aquarists? Simply that we do not know much of anything about whether the trace elements in our aquaria are adequately or excessively bioavailable, regardless of concentration. In fact, reef aquaria might even have situations where there is enough of some metal (say, copper) to kill one organism that can readily absorb the organics that it is bound to, and actually have copper depletion in another organism that is unable to take advantage of that form.
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