Randy's thoughts on trace elements

Randy Holmes-Farley

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Since this topic comes up over and over, I thought I give a summary of my current general thoughts on trace elements for reef aquariums.

1. First, a standard definition. Trace elements are those elements in seawater at very low concentration. It does not include the major ions of seawater: calcium, magnesium, alkalinity (carbonate and bicarbonate), sulfate, potassium, bromide, borate, strontium or fluoride, despite the fact that many commercial trace element supplements may contain some of these. The distinction is important in several ways that will become apparent in subsequent parts of this post, but I'll note here that each of the major ions of seawater are present in concentration above 1 ppm, while all of the other inorganic ions in natural seawater combined is less than 1 ppm total.

2. For major ions, the concentration does not vary by location or depth in the oceans. The only significant variation in major ion concentration comes as the salinity changes. Trace elements, however, are different, and can vary considerably by location and depth. Some are surface depleted. Some are depleted deeper down. No single number, for example, can tell you the natural ocean concentration of, say, iron. If one is targeting a “natural” concentration of iron, what number would one choose? The ocean does not tell us a definitive answer.

3. All organisms need a number of trace elements for a wide range of biochemical processes. These include iron, copper, zinc, manganese, vanadium and molybdenum. Some trace elements are purely a toxicity concern, including mercury, lead, and cadmium. Many are needed at one concentration and are toxic at higher concentration (e.g., copper and nickel). Organisms, such as fish, likely get some or all these needed trace elements from foods rather than from the water itself, but many organisms do get them from the water, and all organisms that do not consume particulate foods in some fashion must do so.

4. For organisms that do get their needed trace elements from the water, there is very little experimental evidence on how much is too little and how much is too much and might be toxic for any given organism. There is a fair amount of experimental evidence in reef aquaria about how much of many trace elements in the typical forms found in reef tanks is “adequate” for the organisms, especially corals, but not really what the acceptable range is. Some of the ICP-based trace element methods use this adequateness approach. In general, reefers have found that the acceptable levels of some trace elements can vary a lot more than the acceptable levels of some major ions. Iron, for example, seems to be able to be acceptable over a very wide range of concentrations (certainly more than a factor of 100) and still be adequately available and not toxic.

5. For major ions, the concentration, and perhaps pH, tells you all you need to know about its bioavailability. 420 ppm calcium is equally bioavailable in every reef tank. Many trace elements, however, can exist in a variety of different chemical forms. These differences include different oxidation states, such as ferric (Fe+++) and ferrous (Fe++) iron. They can also include different complexation by organics. Copper, for example, is known to be nearly entirely bound by organics in the ocean, and that binding greatly impacts (reduces relative to the bare ion) its toxicity and bioavailability. Thus, the concentration of a trace element (such as by any type of ICP) may only provide a part of the question of whether there is enough or too much or too little of a trace element present.

6. The oxidation state and the complexation by organics can change rapidly in a reef aquarium. Thus, the form one doses may immediately change to something else when mixed into the water, and may also change as it experiences various treatments, such as ozone, UV, hydrogen peroxide, antioxidants, processing by organisms, etc.

7. The depletion of trace elements arises in several ways, including uptake by organisms (corals, anemones, algae, bacteria, etc.), binding to mineral surfaces (calcium carbonate, GFO, etc.), and through any sort of organic export mechanism (skimming, activated carbon, polymer resin absorbents, and physical filtering of “detritus”). Many reefers assume that fast growing SPS corals are the driving force behind trace element depletion in their aquaria, but IMO there is little evidence of this. When folks use methods such as macroalgae or turf algae to control nutrients, organic carbon dosing to drive bacteria, skimmers and GAC to export organics, or even particulate calcium carbonate dosing to keep the water clear, these may be equally large or larger sinks for trace elements.

8. Some trace elements have been found to rapidly deplete. These include iron and manganese. They can drop from dosed levels to undetectable by typical hobby testing in a few days. A small amount of macroalgae growth can strip a whole tank of manganese. Some can be much slower to deplete (e.g., zinc). If one chooses to just test the waters of trace element dosing, iron and manganese are a good place to start. There are both DIY and commercial products for just these, and many people have found them useful.

9. Folks thinking about consumption of trace elements in reef tanks often think about water changes as the way they are replaced, and it is true that new trace elements come in with water changes. However, there are additional factors that bear on reef husbandry and our interpretation of the usefulness of our actions.

A. Rapidly depleting trace elements cannot ever be maintained at the concentration in the salt mix by water changes alone unless one changes 100% of the water every day. However, some salt mixes may have more than natural levels of some trace elements, and since the acceptable level of a trace element may be well below that present in the salt mix, water changes may be useful in adding trace elements.

B. A widely ignored source of trace elements may actually be the primary way many trace elements get into reef aquaria. Foods are loaded with trace elements, for the same reason that organisms need to take them up: all organisms and hence all foods sources must contain them. For some, the total amount of certain trace elements (such as iron) may be far higher in daily foods than in daily 100% water changes. However, there are no studies that show how well these food-contained trace elements get into and become part of the food chain in a reef tank. Certainly some is lost, but my expectation is that a substantial amount of trace elements do get into the water this way.

10. Many folks dose trace elements to try to replace those lost in the aquarium, and there are many commercial mixes and DIY recipes. Deciding how much of what to dose is a vexing problem that may be best answered by trial and error (which successfully deals with all of the uncertainties described above) but it takes a lot of time and effort. Folks attempt to shortchange that effort, with a number of different methods that try to eliminate some of the uncertainties, and I’ll describe the pros and cons of these below.

A. Some commercial trace element mixes are designed to be used in a volume dosed per day or week methodology. For example: Add 1 ml of solution to each 100 L of aquarium water daily. Certainly the easiest way for the reefkeeper, but they can only be “perfect” for a single type of reef tank. That said, they may be adequate for a reasonably wide range of reef tanks. A beginning reefer might start here with an additive from a company they have confidence in, since the reefkeeper is fully trusting them to get it right, and IMO, not all companies have earned such trust. One might consider experimenting with lower or higher doses over time to better match the actual needs of your aquarium, and might start high or low if there is more or less growth in general in the aquarium relative to an average tank. A new reef tank with few organisms will certainly take up fewer trace elements, and more is not necessarily better.

B. A second approach ties the amount of trace elements added to the calcification rate. Say, to alkalinity demand per day or calcium demand per day. For example: Add 1ml of supplement for every 20ppm of calcium added per 100 liters of aquarium water. The company makes some sort of determination of the amount of trace elements needed per unit of calcification for a typical reef tank. A number of products do this either explicitly (for a trace supplement) or implicitly, such as with a two part or one part alkalinity and calcium method that has extra added trace elements.
The calcification rate would be a reasonable approach if the tank has about the same consumption characteristics as the tank the product was designed for, but what if it doesn’t? An entirely soft coral tank with a macroalgae refugium and organic carbon dosing may consume more trace elements than a hard coral tank that uses none of these methods. Yet the hard coral tank has far higher calcification and hence is getting more trace elements. This method likely works out for many tanks, but if your tank deviates from a typical mixed tank that the product was likely designed for, it may be a suboptimal way to dose. Again, trust of the company also comes into play. If the method is a stand-alone trace element mix, one might experiment with doses as described in A.

C. A third approach involves testing of the concentrations of many trace elements by ICP (the only way generally available to reefers to test trace elements at low concentrations) and dosing each element measured to bring it back into a desirable range. This method is more expensive and labor intensive than A or B, but is clearly better, in my opinion, without being perfect. The issues include the accuracy of the ICP measurement (may be partly determined by the company and their protocols, partly by the exact type of ICP used, and partly by what happens to the sample between your tank and the plasma itself. Freezing, bacterial growth in the sample tube, binding to the tube sides, any sort of filtration or centrifugation, or lack thereof, at the company may all play a role in the accuracy. Additionally, the issues of chemical speciation (e.g., ferrous vs ferric iron) and complexation by organics is not resolved by ICP. Finally, desirable ranges are often determined by one or more people that may or may not have the same focus (color vs growth, different organisms considered, etc.). I’m also wary of some of these methods that suggest dosing of chemicals not known by science to play any role in any known organisms. If using such a method, I’d either leave these out, or at least experiment by not dosing them and see if anything is different in my aquarium.

11. Do not believe the hype that some commercial products claim about their product boosting specific colors or that specific elements are tied to boosting such colors. Such claims are, in my opinion derived by marketing people and are not based in reef keeping reality. Corals certainly will grow faster and may or may not be more colorful if getting all the trace elements they need, compared to being limited by one or more trace elements, but don’t look to trace elements to take a healthy coral and suddenly make the color pop.

12. Finally, I suggest that silicate dosing can be desirable for many reef aquaria. Yes, that may spur diatoms, but they are no more to be feared in most instances than the green algae they may replace on the glass, and the silicate can allow better growth of sponges that need silicate in the water. While not used by any corals, it may also help prevent dinoflagellate infestations by allowing diatoms to cover bare surfaces and outcompete the dinos.

There is, of course, far more to trace elements than described here, and I have not really intended this as a cookbook directive, but rather to help folks gain a wider appreciation of what the trace element world of reefing currently comprises.

Happy Reefing!
 
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Troylee

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Great article Randy! Do you consider iodine a trace element? I notice almost every icp test anyone gets it’s low! I started adding 2 drops of lugols a day to my tank and what a world of difference it has made!
 
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Randy Holmes-Farley

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I consider it a minor element, but some definitions do consider it a trace element. But that difference is just semantic.

What difference did you observe?
 

Troylee

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I consider it a minor element, but some definitions do consider it a trace element. But that difference is just semantic.

What difference did you observe?
I started dosing it cause I have a bunch of shrimps who molt obviously and I saw people always seem to be low on icp. Anywho for some weird reason my sps started getting crazy polyp extension and just much more fuzzier overall in just one week of dosing it. I’ve had some for close to a year with normal pe during the day that are reaching For the stars now, all day and night lol..
 

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To point #12 with silica dosing

My first reef tank had sand I collected from a beach on the coast of GA. That sand has a lot of silica in it. I was constantly cleaning diatoms off the glass but had plenty of sand sifters and snails to keep the rock clean. I never had issues with dinos, even with multiple moves the tank and keeping the same sand bed each time. Sand bed was 4-5 inches deep in a 36 bowfront
 

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Thanks Randy.

Lot to digest in this article. Just thinking about what trace elements are and how they may affect both fish and coral makes my head spin. So many factors (not just chemistry) affect the health of the life within the tank I can't comprehend how to evaluate the impact an individual trace element may have. The difference between anecdotal and true scientific evidence, as is the case with many of the concerns in the hobby, is difficult to discern.

Will be interesting to see what shakes out in the discussion.
 

Reefkeepers Archive

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Great article! Have to agree that the "dose this per 25 gallons" or "1 ml for blank calcium used" isn't a one size fits all. I use red sea trace colors pro 4 part dosing to replenish trace elements as I don't do water changes. I only dose .5 ml of potassium daily, but 1 ml of iodine and 2ml of what's labeled as "bioactive elements" which are things like strontium and other such elements I assume, but I do 3 ml daily iron. I do test for these with a hobby grade test kit occasionally and they are usually within range
 
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Randy Holmes-Farley

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I started dosing it cause I have a bunch of shrimps who molt obviously and I saw people always seem to be low on icp. Anywho for some weird reason my sps started getting crazy polyp extension and just much more fuzzier overall in just one week of dosing it. I’ve had some for close to a year with normal pe during the day that are reaching For the stars now, all day and night lol..

I'm not convinced shrimp need any iodine, and I think the molting is not necessarily a positive response.

Curiously, a need for iodine in the water is not once mentioned by the aquaculture of shrimp industry.

I do not detect difference in the years I dosed iodide vs later years when i did not.

There are a few corals with a known scientific need for iodine, such as certain gorgionia. I detail those in one of my iodine articles, but otherwise, there's no scientifically demonstrated need in most corals.

Chemistry And The Aquarium: Iodine in Marine Aquaria: Part I ? Advanced Aquarist | Aquarist Magazine and Blog

Chemistry And The Aquarium: Iodine In Reef Tanks 2: Effects On Macroalgae Growth ? Advanced Aquarist | Aquarist Magazine and Blog

That said, i recognize that enough people find a benefit when dosing that I am open to the idea that it is useful for more corals than have a known need.

Finally, Lugols is especially complicated to interpret. It comes partly in a highly oxidizing form (I2) which will react with many things, including other trace elements (which has been known for 100 years), converting them to other oxidation states and possibly changing the bioavailability of them.
 
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Randy Holmes-Farley

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To point #12 with silica dosing

My first reef tank had sand I collected from a beach on the coast of GA. That sand has a lot of silica in it. I was constantly cleaning diatoms off the glass but had plenty of sand sifters and snails to keep the rock clean. I never had issues with dinos, even with multiple moves the tank and keeping the same sand bed each time. Sand bed was 4-5 inches deep in a 36 bowfront

When I first began delving into silicate and silica, I was hit by a wall of "it cannot happen" from folks reading somewhere that quartz is insoluble so it cannot dissolve (same for alumina, but that's a different story).

It ended up being easier to measure it than to try to convince many folks it was possible.

Here's the section of my silicate article on quartz sand:


The Dissolution of Quartz Sand​

One of the issues that has been floating around the reef keeping hobby for a long time is the issue of whether “silica” sand actually releases soluble silica or not. It is remarkable that so many people have strong opinions on this issue, and yet so few people have ever bothered to do the easy experiment of measuring it. Many even fall for the trap of concluding that since their glass aquarium is not dissolving, then silica sand must not be either. All of the arguments against soluble silica being released from “silica” sand can be easily refuted, and I have done so in the past, but that is not the point of this article. Still, some background is worthwhile before getting to experimental results.

Silica sand is largely composed of quartz. Quartz has a maximum solubility in pure freshwater of about 180 uM (11 ppm as SiO2)36, and is somewhat higher in seawater.37 That value is substantially in excess of the dissolved silica concentrations in any normal part of the ocean (excluding plumes from vents from hot springs and such). So why doesn’t quartz beach sand dissolve? It does, but it does so very slowly. The rate of dissolution of quartz has been studied, and it is very slow. 38 It is the slow dissolution of quartz, not the solubility itself, which allows it to remain on many ocean beaches.

A final comment on quartz sand is that it is known that organic acids can increase the rate of dissolution of quartz by at least a factor of ten.39 This may be especially applicable in reef tanks, where organic materials may be in abundance, particularly when organisms are living directly on the sand, potentially releasing such acids directly onto the sand surface.

The problem with extrapolating from the known very slow rate of dissolution of quartz to “silica sand” is that it simply is not pure quartz. The dissolution of soluble silica from “quartz sand” (98.5% SiO2) has long been known to exceed the solubility of quartz itself.40 Take a close look at some commercial “silica” sand. It isn’t even close to being white, which an absolutely pure quartz sand will be. There are all sorts of different colored particulates in it (some are even magnetic and can be picked out with a magnet). Without going into detail on mineralogy, suffice to say that there are many minerals that readily dissolve to release silicate into the water. Such dissolution is why freshwater rivers contain so much silica (typically 150 uM (9 ppm SiO2)).4 Your sand claims to be 98% quartz? What about that other 2%? Two percent of a 50-pound bag of sand is a pound of “other stuff”.

If you start with true beach sand, and don’t fracture it much, then it is very likely that you will detect little dissolution of silica from it in a few days (although I’ve not tried it), because most of the readily dissolved minerals would have disappeared long ago (or are trapped inside). But commercial play sands are not typically from beaches, and are not collected with any kind of gentleness. They are often mined from sand pits, crushed, screened, and generally treated rather roughly. This serves to break many of the grains, exposing new mineral inclusions that are then primed to dissolve. This source is, in my opinion, where most of the soluble silica comes from in “silica” sand.

So, on to some experiments. I bought some Quickcrete Play Sand from Home Depot and ran a number of tests on it. In all of the cases shown below the silica concentration was determined with a Hach low range silica kit after filtration through a 0.2 mm syringe filter. In cases where the concentration is above 1 ppm, the sample was diluted with RO/DI water prior to analysis. All experiments were carried out in the dark to reduce any effect due to diatom growth.

In the first experiment I took 3 cups of sand, and suspended it in 3 gallons of freshly made Instant Ocean salt mix that initially contained less than 0.8 uM of silica (0.05 ppm SiO2). After 48 hours of gentle stirring with a powerhead (the water was stirring, but not the sand), the silica concentration had risen to 17 uM (1.0 ppm SiO2).

I then rinsed the same sand 5 times with 1 gallon RO/DI water (1 minute each time), discarded the contents, and then ran the same stirring experiment with 2 new gallons of Instant Ocean salt mix. In 48 hours the silica concentration had again risen, this time to 15 uM (0.92 ppm SiO2). Then I let it sit unstirred for another 96 hours, and the concentration had risen more, to 23 uM (1.4 ppm SiO2).

In a different experiment, I took about 45 pounds of sand, and added 2 gallons of Instant Ocean salt mix. I let this mixture sit for 7 days, with once a day mixing with my hands for about 30 seconds. At then end of this test, the concentration was 90 uM (5.4 ppm SiO2).

It has been suggested that the amount of silica coming from calcerous sand might actually be as high or higher than that from silica sand. To test this hypothesis, I repeated the small-scale experiments above on a calcium carbonate sand from Home Depot (Southdown). In this case, there was some soluble silica released after the first 48 h, but only 1.6 uM (0.1 ppm SiO2), or about a factor of 10 lower than the silica sand. In a long-term test, the concentration had only risen to 5 uM (0.3 ppm SiO2) in 14 days with once a day stirring.

From these experiments, I conclude that:

  1. The “silica” play sand that I purchased from Home Depot can substantially raise the dissolved silica concentration in seawater.
  2. The dissolvable portion of the silica sand cannot be completely removed by several rinses with either fresh or salt water, although it may be decreased somewhat by that process.
  3. Southdown calcium carbonate sand (likely aragonite) can release soluble silica, but about ten fold less than the “silica” sand.
Is it OK to use silica sand? Probably. Many people do so. I also believe that not all “silica “ sands will be the same for the reasons described above relating to processing of the sand and the nature of the mineral inclusions present. So the fact that many people successfully use some (or many) types of silica sand does not necessarily imply that all people can use any type of “silica” sand without a problem.
 

Troylee

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I'm not convinced shrimp need any iodine, and I think the molting is not necessarily a positive response.

Curiously, a need for iodine in the water is not once mentioned by the aquaculture of shrimp industry.

I do not detect difference in the years I dosed iodide vs later years when i did not.

There are a few corals with a known scientific need for iodine, such as certain gorgionia. I detail those in one of my iodine articles, but otherwise, there's no scientifically demonstrated need in most corals.

Chemistry And The Aquarium: Iodine in Marine Aquaria: Part I ? Advanced Aquarist | Aquarist Magazine and Blog

Chemistry And The Aquarium: Iodine In Reef Tanks 2: Effects On Macroalgae Growth ? Advanced Aquarist | Aquarist Magazine and Blog

That said, i recognize that enough people find a benefit when dosing that I am open to the idea that it is useful for more corals than have a known need.

Finally, Lugols is especially complicated to interpret. It comes partly in a highly oxidizing form (I2) which will react with many things, including other trace elements (which has been known for 100 years), converting them to other oxidation states and possibly changing the bioavailability of them.
Interesting! Yeah the only thing I’ve noticed is increased pe for some odd reason! Nothing else has changed in my tank and all the sticks got super fuzzy!
 
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Randy Holmes-Farley

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Great article! Have to agree that the "dose this per 25 gallons" or "1 ml for blank calcium used" isn't a one size fits all. I use red sea trace colors pro 4 part dosing to replenish trace elements as I don't do water changes. I only dose .5 ml of potassium daily, but 1 ml of iodine and 2ml of what's labeled as "bioactive elements" which are things like strontium and other such elements I assume, but I do 3 ml daily iron. I do test for these with a hobby grade test kit occasionally and they are usually within range

Thanks! :)
 

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Recall learning about trace elements in the 80s or 90s yet no way of testing them thereby I just lost track of them. Fast forward to ICP and Triton then the Dutch version and now Moonshiners and this is one rabbit hole I may never surface from again.

Two options, being best fit for my life style. Dose AFR, test Iron and supplement with ChartoGro or other options and add Tropic Marin A&K based on which ever single element is predominant off ICP and roll the dice from their. No WC. I’ll live with the consequences

Second option. Move to the keys. Live on the water. Replace tank contents daily after sediment filtration down to 0.025 microns followed by ozone/hydrogen peroxide and UV. Fingers crossed no oil spills near me or other catastrophes my raw water filtration can’t remove. Best part. Can be fully automated and when I get sick of my fish. Go native and add them or just go for a swim and see new and unique.

Reefing shouldn’t be this exhausting. Dose this. Test that. Remove what was overdosed. Makes you want to self dose vodka and Red Bull knowing in a short while you will not care and next morning you will not remember you ever cared
 
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This thread is for the general discussion of the Article Randy's thoughts on trace elements. Please add to the discussion here.
I liked the bullet point style of writing. The article gathers in one place what you have been advising us over the years. Thanks for this.

My trace element story is simple. Up the dose of CheatoGro when the Ulva feels like blanched spinach. Lower the dose if the snails stop moving.
 
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Randy Holmes-Farley

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I liked the bullet point style of writing. The article gathers in one place what you have been advising us over the years. Thanks for this.

My trace element story is simple. Up the dose of CheatoGro when the Ulva feels like blanched spinach. Lower the dose if the snails stop moving.
Thanks. That was the goal: put it into one place for folks coming along to see it without having to read a dozen different discussions.

I wonder what the range is between blanched spinach and lethargic snails. lol
 

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Thanks Randy,

I like number 11 and that you are calling these manufacturers out on the bs.

No one really knows, except Mother Nature.

I use NSW despite the concern of others for parasites, bacteria, contaminates etc.. I always thought it was the same water whether I got it from the inlet, the beach, or offshore.

Long time ago I met a couple guys raking up bags of sargassum from the beach. I asked and turns out they use it for flower beds, roses. The older gentleman said it has everything in it, even gold. How true that is I don’t know.
This leads to another belief, hunch, suspicion about food. 9B. Nori, other macro algae would contain trace elements. I feed oyster slurry to the tank as well and the fish love it. . I posted a thread a while ago asking about the nutritional value, amino acids found in oysters. I don’t remember the exact response but it falls under 9B.

I have been dosing silicates, ammonia, iron/manganese occasionally, lugols on/off, vinegar. The only one I am not sure is beneficial is the Lugol’s. Nothing “bad” has ever occurred from it and have used it for many years.

Kalkwasser in ATO and occasional bump with soda ash and calcium chloride. I made diy solutions from your postings however don’t use them. Fear is a healthy in this case.

The old saying only dose what you can test for is no longer. There were many successful, beautiful tanks before all the fancy hardware and additives
 

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Great article Randy! Do you consider iodine a trace element? I notice almost every icp test anyone gets it’s low! I started adding 2 drops of lugols a day to my tank and what a world of difference it has made!
Whats the difference? Color? Growth?
 

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Thank you so much, Dr. Randy!

I enjoyed reading this article. I haven’t noticed any change from dosing iodide in my tank. I dosed it to see if my Goniopora would appreciate it.

Trace elements are far too complicated and a fickle beast. We don’t know enough about them.

I try to dose 5mL of Tropic Marin K+ to my 260 gallon tank once a week. I am not religious about it at all. Judging by the growth and color of my hair algae, I think I’m doing fine lol.
 

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Thanks once again Randy, for all the time you spend explaining the mysteries of Saltwater Reefing! You help a lot of people on this site and your time and knowledge are appreciated.
 

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Since this topic comes up over and over, I thought I give a summary of my current general thoughts on trace elements for reef aquariums.

1. First, a standard definition. Trace elements are those elements in seawater at very low concentration. It does not include the major ions of seawater: calcium, magnesium, alkalinity (carbonate and bicarbonate), sulfate, potassium, bromide, borate, strontium or fluoride, despite the fact that many commercial trace element supplements may contain some of these. The distinction is important in several ways that will become apparent in subsequent parts of this post, but I'll note here that each of the major ions of seawater are present in concentration above 1 ppm, while all of the other inorganic ions in natural seawater combined is less than 1 ppm total.

2. For major ions, the concentration does not vary by location or depth in the oceans. The only significant variation in major ion concentration comes as the salinity changes. Trace elements, however, are different, and can vary considerably by location and depth. Some are surface depleted. Some are depleted deeper down. No single number, for example, can tell you the natural ocean concentration of, say, iron. If one is targeting a “natural” concentration of iron, what number would one choose? The ocean does not tell us a definitive answer.

3. All organisms need a number of trace elements for a wide range of biochemical processes. These include iron, copper, zinc, manganese, vanadium and molybdenum. Some trace elements are purely a toxicity concern, including mercury, lead, and cadmium. Many are needed at one concentration and are toxic at higher concentration (e.g., copper and nickel). Organisms, such as fish, likely get some or all these needed trace elements from foods rather than from the water itself, but many organisms do get them from the water, and all organisms that do not consume particulate foods in some fashion must do so.

4. For organisms that do get their needed trace elements from the water, there is very little experimental evidence on how much is too little and how much is too much and might be toxic for any given organism. There is a fair amount of experimental evidence in reef aquaria about how much of many trace elements in the typical forms found in reef tanks is “adequate” for the organisms, especially corals, but not really what the acceptable range is. Some of the ICP-based trace element methods use this adequateness approach. In general, reefers have found that the acceptable levels of some trace elements can vary a lot more than the acceptable levels of some major ions. Iron, for example, seems to be able to be acceptable over a very wide range of concentrations (certainly more than a factor of 100) and still be adequately available and not toxic.

5. For major ions, the concentration, and perhaps pH, tells you all you need to know about its bioavailability. 420 ppm calcium is equally bioavailable in every reef tank. Many trace elements, however, can exist in a variety of different chemical forms. These differences include different oxidation states, such as ferric (Fe+++) and ferrous (Fe++) iron. They can also include different complexation by organics. Copper, for example, is known to be nearly entirely bound by organics in the ocean, and that binding greatly impacts (reduces relative to the bare ion) its toxicity and bioavailability. Thus, the concentration of a trace element (such as by any type of ICP) may only provide a part of the question of whether there is enough or too much or too little of a trace element present.

6. The oxidation state and the complexation by organics can change rapidly in a reef aquarium. Thus, the form one doses may immediately change to something else when mixed into the water, and may also change as it experiences various treatments, such as ozone, UV, hydrogen peroxide, antioxidants, processing by organisms, etc.

7. The depletion of trace elements arises in several ways, including uptake by organisms (corals, anemones, algae, bacteria, etc.), binding to mineral surfaces (calcium carbonate, GFO, etc.), and through any sort of organic export mechanism (skimming, activated carbon, polymer resin absorbents, and physical filtering of “detritus”). Many reefers assume that fast growing SPS corals are the driving force behind trace element depletion in their aquaria, but IMO there is little evidence of this. When folks use methods such as macroalgae or turf algae to control nutrients, organic carbon dosing to drive bacteria, skimmers and GAC to export organics, or even particulate calcium carbonate dosing to keep the water clear, these may be equally large or larger sinks for trace elements.

8. Some trace elements have been found to rapidly deplete. These include iron and manganese. They can drop from dosed levels to undetectable by typical hobby testing in a few days. A small amount of macroalgae growth can strip a whole tank of manganese. Some can be much slower to deplete (e.g., zinc). If one chooses to just test the waters of trace element dosing, iron and manganese are a good place to start. There are both DIY and commercial products for just these, and many people have found them useful.

9. Folks thinking about consumption of trace elements in reef tanks often think about water changes as the way they are replaced, and it is true that new trace elements come in with water changes. However, there are additional factors that bear on reef husbandry and our interpretation of the usefulness of our actions.

A. Rapidly depleting trace elements cannot ever be maintained at the concentration in the salt mix by water changes alone unless one changes 100% of the water every day. However, some salt mixes may have more than natural levels of some trace elements, and since the acceptable level of a trace element may be well below that present in the salt mix, water changes may be useful in adding trace elements.

B. A widely ignored source of trace elements may actually be the primary way many trace elements get into reef aquaria. Foods are loaded with trace elements, for the same reason that organisms need to take them up: all organisms and hence all foods sources must contain them. For some, the total amount of certain trace elements (such as iron) may be far higher in daily foods than in daily 100% water changes. However, there are no studies that show how well these food-contained trace elements get into and become part of the food chain in a reef tank. Certainly some is lost, but my expectation is that a substantial amount of trace elements do get into the water this way.

10. Many folks dose trace elements to try to replace those lost in the aquarium, and there are many commercial mixes and DIY recipes. Deciding how much of what to dose is a vexing problem that may be best answered by trial and error (which successfully deals with all of the uncertainties described above) but it takes a lot of time and effort. Folks attempt to shortchange that effort, with a number of different methods that try to eliminate some of the uncertainties, and I’ll describe the pros and cons of these below.

A. Some commercial trace element mixes are designed to be used in a volume dosed per day or week methodology. For example: Add 1 ml of solution to each 100 L of aquarium water daily. Certainly the easiest way for the reefkeeper, but they can only be “perfect” for a single type of reef tank. That said, they may be adequate for a reasonably wide range of reef tanks. A beginning reefer might start here with an additive from a company they have confidence in, since the reefkeeper is fully trusting them to get it right, and IMO, not all companies have earned such trust. One might consider experimenting with lower or higher doses over time to better match the actual needs of your aquarium, and might start high or low if there is more or less growth in general in the aquarium relative to an average tank. A new reef tank with few organisms will certainly take up fewer trace elements, and more is not necessarily better.

B. A second approach ties the amount of trace elements added to the calcification rate. Say, to alkalinity demand per day or calcium demand per day. For example: Add 1ml of supplement for every 20ppm of calcium added per 100 liters of aquarium water. The company makes some sort of determination of the amount of trace elements needed per unit of calcification for a typical reef tank. A number of products do this either explicitly (for a trace supplement) or implicitly, such as with a two part or one part alkalinity and calcium method that has extra added trace elements.
The calcification rate would be a reasonable approach if the tank has about the same consumption characteristics as the tank the product was designed for, but what if it doesn’t? An entirely soft coral tank with a macroalgae refugium and organic carbon dosing may consume more trace elements than a hard coral tank that uses none of these methods. Yet the hard coral tank has far higher calcification and hence is getting more trace elements. This method likely works out for many tanks, but if your tank deviates from a typical mixed tank that the product was likely designed for, it may be a suboptimal way to dose. Again, trust of the company also comes into play. If the method is a stand-alone trace element mix, one might experiment with doses as described in A.

C. A third approach involves testing of the concentrations of many trace elements by ICP (the only way generally available to reefers to test trace elements at low concentrations) and dosing each element measured to bring it back into a desirable range. This method is more expensive and labor intensive than A or B, but is clearly better, in my opinion, without being perfect. The issues include the accuracy of the ICP measurement (may be partly determined by the company and their protocols, partly by the exact type of ICP used, and partly by what happens to the sample between your tank and the plasma itself. Freezing, bacterial growth in the sample tube, binding to the tube sides, any sort of filtration or centrifugation, or lack thereof, at the company may all play a role in the accuracy. Additionally, the issues of chemical speciation (e.g., ferrous vs ferric iron) and complexation by organics is not resolved by ICP. Finally, desirable ranges are often determined by one or more people that may or may not have the same focus (color vs growth, different organisms considered, etc.). I’m also wary of some of these methods that suggest dosing of chemicals not known by science to play any role in any known organisms. If using such a method, I’d either leave these out, or at least experiment by not dosing them and see if anything is different in my aquarium.

11. Do not believe the hype that some commercial products claim about their product boosting specific colors or that specific elements are tied to boosting such colors. Such claims are, in my opinion derived by marketing people and are not based in reef keeping reality. Corals certainly will grow faster and may or may not be more colorful if getting all the trace elements they need, compared to being limited by one or more trace elements, but don’t look to trace elements to take a healthy coral and suddenly make the color pop.

12. Finally, I suggest that silicate dosing can be desirable for many reef aquaria. Yes, that may spur diatoms, but they are no more to be feared in most instances than the green algae they may replace on the glass, and the silicate can allow better growth of sponges that need silicate in the water. While not used by any corals, it may also help prevent dinoflagellate infestations by allowing diatoms to cover bare surfaces and outcompete the dinos.

There is, of course, far more to trace elements than described here, and I have not really intended this as a cookbook directive, but rather to help folks gain a wider appreciation of what the trace element world of reefing currently comprises.

Happy Reefing!
Wish you would cut it down with a concussion at the end, I.e . I makes sense to dose trace elements or in general just feed the fish
 

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