Essential trace elements may mean to hobby supply companies impurities that they cannot remove (good or bad
), but if added to limewater, they may settle out on the bottom anyway. I don't recommend most trace elements as a supplement, but if you do, keep them out of the limewater.
IMO, I'd recommend most any food grade lime, or any of several hobby brands.
I discuss grades of lime here:
What Your Grandmother Never Told You About Lime
http://reefkeeping.com/issues/2005-01/rhf/index.htm
I discuss trace elements here:
The “How To†Guide to Reef Aquarium Chemistry for Beginners, Part 2: What Chemicals Must be Supplemented
http://reefkeeping.com/issues/2007-04/rhf/index.php
specifically here:
http://reefkeeping.com/issues/2007-04/rhf/index.php#20
Trace Element Mixtures
Trace elements are one of the most confusing areas of seawater chemistry, for hobbyists and chemical oceanographers alike. For oceanographers they are complicated because they are hard to measure at such low levels, and they are often bound to organics, making their bioavailability depend as much on how they are bound as on their concentration. For example, knowing the absolute concentration of copper does not necessarily say whether it is so bioavailable as to be toxic, or so tightly bound to chelating organics as to limit growth by unavailability.
Many hobbyists are confused about what trace elements even are, which is not surprising because manufacturers and hobbyists alike often use the term willy nilly. Trace elements are those that are present at very low levels, i.e., less than 50 nM (nanomolar; about 1-10 parts per billion or so, depending on the size of the ion). Most of the trace elements in seawater are heavy metals, and some can be nutritionally required, but most can also be toxic at higher than natural levels (copper, for example, fits that description).
Definitions aside, we need to address the utility of the ions that are put into such supplements, regardless of whether they are trace elements or something else. But there are important dosing differences that relate to whether something is a trace element or not. Notably, if something is normally present at very low concentrations, it takes only a tiny bit of it to bring a depleted aquarium up to seawater's concentration. That is not so for a major ion, which might require far larger doses to bring it to normal concentrations. To boost magnesium in natural seawater by 10% in a 100-gallon aquarium, for example, would take ¾ of a pound of the most potent solid dry supplement. By comparison, to boost iron by 10% in 100 gallons of natural seawater takes a dose so small that you might not see it if it were sitting in a spoon (far less than a milligram).
Perhaps the best way to discuss such mixtures is to dissect a typical commercial example. I’ve chosen one not because it is any better or worse than the others, but because it is widely sold and actually lists its ingredients - Kent Essential Elements. Kent claims, “Kent Marine Essential Elements replaces biologically important trace minerals which are removed by…†The ingredient list shows, “Contents: Inorganic mineral salts of aluminum, boron, bromine, calcium, chromium, cobalt, copper, iodine, iron, lithium, magnesium, manganese, molybdenum, nickel, potassium, selenium, sulfur, strontium, tin, vanadium, and zinc in a base containing deionized water and EDTA.â€Â
Which of those are actually trace elements in natural seawater? Many are not. Magnesium is the third most abundant ion in seawater. Sulfur (as sulfate) is fourth. Not calcium, or potassium, or boron, or bromine, or strontium - all of which are major ions. There is nothing wrong with major ions, but there is no reason to think that they all need to be supplemented, or that a teaspoon of this liquid could contain enough of each to even detect once diluted into a tank (the recommended dose is one teaspoon per 50 gallons per week). Even if this product contained as much magnesium as a typical commercial magnesium supplement (it likely has far less), that teaspoon could boost magnesium by only 1 ppm; not enough to write home about. When major ions need to be boosted, the amounts present in a trace element mixture such as this one may not be enough to be important. To Kent’s credit, the company states that on its website for at least some of the ions in this supplement, notably strontium, iodine and calcium, when users are directed to Kent's other products. Don’t be fooled into thinking, “Some is better than none, so I might as well dose it.†If you have a shortage of a major ion, which you confirmed by testing, you should look for a better way to solve that problem than a trace element mixture.
Working our way down the ingredient list for our prototypical trace element mixture, iodine, lithium and manganese are minor ions, not trace elements. I mentioned above that I don’t recommend supplementing iodine, but if you want to I definitely don’t recommend using an unknown form of iodine at an unknown concentration. According to the well-respected salt mix analysis by Atkinson and Bingman, lithium is elevated substantially above natural levels in every tested salt mix. According to a reef tank water study by Ron Shimek, the average lithium level was several-fold higher than natural levels. Because lithium offers little in the way of known nutritional benefits to marine organisms, it seems to be an undesirable ingredient. Manganese might well be a useful additive, because it is nutritionally important. But little useful data are available on its concentration in reef aquaria, so users cannot know whether the amount in the supplement is appropriate or not.
That leaves the true trace elements aluminum, chromium, cobalt, copper, iron, molybdenum, nickel, selenium, tin, vanadium and zinc. Of course, despite Kent's claims that the supplement “does not contain detrimental heavy metals,†some of these are potentially toxic heavy metals with no known positive biological function (nickel and tin, for example). Why put them into your aquarium? Others are clearly detrimental if “too much†is added (copper, for example). The company presumably does not add “too much†of these to its supplement.
So, we are left with a few trace elements that may have a benefit. Iron could be beneficial, if enough is there; of course, Kent does not say how much is there. Aluminum is very unlikely to be beneficial, as are nickel and tin. Some could be beneficial if the aquarium were depleted of them; zinc, for example. But what if their levels are already elevated in the aquarium? According to a reef aquarium water study by Ron Shimek, some of these are already elevated above natural levels in most reef aquaria. Admittedly, that does not mean that more could not be beneficial. But what is the evidence that more is good? Despite no intentional additions, my aquarium has levels of copper well above natural seawater. How does Kent know that my organisms would benefit from more? And how did Kent determine the relative amounts of different ions in this supplement? What are those amounts? If I did want one of these, how do I know I’m getting enough?
To me this seems like playing a chess game with every piece rigidly connected. They all move together, whether you want them to or not. Worse yet, you don’t know what the move actually is because Kent decided, but does not reveal it to you. It seems like a poor way to manage an aquarium.
In short, I do not recommend trace element mixtures. If you believe that you need (or want to experiment with) trace elements (such as iron or manganese), my suggestion is to use single additives of known concentrations.
These articles have more information that relates to trace elements, although beware that some of them contain errors of various sorts:
What is Seawater?
http://reefkeeping.com/issues/2005-11/rhf/index.php
It’s (In) the Water
http://www.reefkeeping.com/issues/2002-02/rs/feature/index.php
It’s Still (In) the Water
http://www.reefkeeping.com/issues/2002-03/rs/feature/index.php
A Chemical Analysis of Select Trace Elements in Synthetic Sea Salts and Natural Seawater
http://www.advancedaquarist.com/issues/sept2004/feature.htm
Inland Reef Aquaria Salt Study, Part I
http://www.advancedaquarist.com/2005/11/aafeature1
Inland Reef Aquaria Salt Study Part II
http://www.advancedaquarist.com/2005/12/aafeature1
Toxicity of Trace Elements: Truth or Myth?
http://www.advancedaquarist.com/issues/may2003/feature.htm
Aluminum and Aluminum-based Phosphate Binders
http://www.advancedaquarist.com/issues/july2003/chem.htm
Reef Aquaria with Low Soluble Metals
http://www.reefkeeping.com/issues/2003-04/rhf/feature/index.php
First Iron Article: Macroalgae and Dosing Recommendations
http://www.advancedaquarist.com/issues/aug2002/chem.htm
Second Iron Article: Iron: A Look at Organisms Other than Macroalgae
http://www.advancedaquarist.com/issues/oct2002/chem.htm
