Randy's thoughts on trace elements

[Randy Holmes-Farley]

I certainly have no concerns with feeding many types of organic phosphates, either particulate or dissolved, but it can be trickier since those forms are not measurable with typical home test kits, so one has to go by tank appearance, ICP (without a real benchmark to compare to), or trusting someone else's dose.

 

[tmo65]

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!

How large is your tank? I get very little polyp extension and would like to experiment slowly. Two drops for a tank of what size?

Thanks.

 

[Troylee]

How large is your tank? I get very little polyp extension and would like to experiment slowly. Two drops for a tank of what size?

Thanks.

300 gallon. It’s about 260 wet with the sump.

 

[drbrivers]

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:

Silica In Reef Aquariums

Why would I recommend dosing silica? Largely because creatures in our tanks use it, the concentrations in our tanks (at least in mine) are below natural levels, and the sponges, mollusks, and diatoms may not be getting enough to thrive.

reefs.com

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.

Just now had a chance to read this - another great article as usual. Many thanks. Happy New Year too.

 

[Randy Holmes-Farley]

Just now had a chance to read this - another great article as usual. Many thanks. Happy New Year too.

Thanks. Happy Reefing.

 

[drbrivers]

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!

Dear Randy - Would you at some point do a write up on what test kits and other measuring devices that you have found would be good for marine aquaria ? Thanks

 

[acro_lover]

Amazing article. Very informative.
Here is how we dose:

Trace Element: Essential for Acropora Reef Tanks - ACROKINGDOM

Discover why trace element are vital for a thriving reef tank. Learn how they promote coral growth and enhance vibrancy.

acrokingdom.com

 

[acro_lover]

Hi @Randy Holmes-Farley
I'm hoping you can help me with a mystery. Last week, I purchased a new jar of sodium fluoride. I still haven't finished the old one, but since I was placing a large order, I thought it would be smart to get a new one, as humidity might have compromised the old jar. I've been dissolving 4 grams in 1 liter of RODI water for many years, but I'm having trouble with the new jar. Most of the sodium fluoride just settles at the bottom of the bottle and doesn't dissolve. It's really concerning me. The old jar contains a powdery substance, while the new one looks more like cooking salt. Do you have any ideas about why this might be happening?

 

[Randy Holmes-Farley]

Hi @Randy Holmes-Farley
I'm hoping you can help me with a mystery. Last week, I purchased a new jar of sodium fluoride. I still haven't finished the old one, but since I was placing a large order, I thought it would be smart to get a new one, as humidity might have compromised the old jar. I've been dissolving 4 grams in 1 liter of RODI water for many years, but I'm having trouble with the new jar. Most of the sodium fluoride just settles at the bottom of the bottle and doesn't dissolve. It's really concerning me. The old jar contains a powdery substance, while the new one looks more like cooking salt. Do you have any ideas about why this might be happening?

What concentration are you trying to make it?

This is in ro/di, right?

 

[acro_lover]

What concentration are you trying to make it?

This is in ro/di, right?

@Randy Holmes-Farley yes, rodi.
4gr in 1L RODI

 

[WhatCouldGoWrong71]

@Randy Holmes-Farley yes, rodi.
4gr in 1L RODI

Following.

Is 1gr to 1 liter the standard mixing ratio? I just ordered the below and am about to start mixing my own as to not spend $20 for 500ml (Moonshine). I’m going through 2L a month.

 

[Randy Holmes-Farley]

@Randy Holmes-Farley yes, rodi.
4gr in 1L RODI

Solubility is ten times that amount. I think there must be an impurity issue.

 

[acro_lover]

Thats what i thought but wanted to doublecheck. I will check with the manufacturer.
@Randy Holmes-Farley , can i please ask one more question. Can you please check my math for the

Strontium Chloride Hexahydrate 98%​

Strontium Chloride Hexahydrate should be 45.5% strontium by weight.​

Dissolving 1g in 1 L of ro/di gives 0.455 mg/mL

Adding 1 mL to 100 L of tank volume boosts strontium by 0.45 mg/100 L

Is that correct? Or Am i wrong?
Thanks a lot.

 

[Lasse]

1 mole of Strontium Chloride Hexahydrate (SrCl2 · 6H2O) is 266.62 g
1 mole of strontium (Sr) = 87.6 g
87.6/266.62 = 0.328557 -> around 33 % if I´m not calculate wrong

Sincerely Lasse

 

[KStatefan]

Following.

Is 1gr to 1 liter the standard mixing ratio? I just ordered the below and am about to start mixing my own as to not spend $20 for 500ml (Moonshine). I’m going through 2L a month.

Who's Standard?

I use a 1000 ppm Fluoride solution by making 500 ml volume solution with 1.1 grams NaF

 

[WhatCouldGoWrong71]

Who's Standard?

I use a 1000 ppm Fluoride solution by making 500 ml volume solution with 1.1 grams NaF

Moonshine.

 

[KStatefan]

Moonshine.

I think their solution is 1000 ppm.

@Formulator has a calculator posted here that you can use to calculate the concentration

 

[acro_lover]

Thats what i thought but wanted to doublecheck. I will check with the manufacturer.
@Randy Holmes-Farley , can i please ask one more question. Can you please check my math for the

Strontium Chloride Hexahydrate 98%​

Strontium Chloride Hexahydrate should be 45.5% strontium by weight.​

Dissolving 1g in 1 L of ro/di gives 0.455 mg/mL

Adding 1 mL to 100 L of tank volume boosts strontium by 0.45 mg/100 L

Is that correct? Or Am i wrong?
Thanks a lot.

@Randy Holmes-Farley whenever you get a chance, can you please let me know if you think my math is correct? Thank you so much

 

[Randy Holmes-Farley]

@Randy Holmes-Farley whenever you get a chance, can you please let me know if you think my math is correct? Thank you so much

Sure. I did not follow up because Lasse's correction is accurate.

Strontium chloride hexahydrate is 33% strontium by weight.


Dissolving 1g in 1 L of ro/di gives 0.33 mg/mL Sr++

Adding 1 mL to 100 L of tank volume boosts strontium by 0.33 mg/100 L = 0.0033 mg/L (ppm)

 

[acro_lover]

Sure. I did not follow up because Lasse's correction is accurate.

Strontium chloride hexahydrate is 33% strontium by weight.


Dissolving 1g in 1 L of ro/di gives 0.33 mg/mL Sr++

Adding 1 mL to 100 L of tank volume boosts strontium by 0.33 mg/100 L = 0.0033 mg/L (ppm)

Thanks a lot @Randy Holmes-Farley . Just wanted to double check.
Where do you check the weight of the individual elements? Is there a book or a web page?
Cause if i simply goodle it i get 45.5% ( please see screenshot attached)
just want to learn how to check those things properly

Sure. I did not follow up because Lasse's correction is accurate.

Strontium chloride hexahydrate is 33% strontium by weight.


Dissolving 1g in 1 L of ro/di gives 0.33 mg/mL Sr++

Adding 1 mL to 100 L of tank volume boosts strontium by 0.33 mg/100 L = 0.0033 mg/L (ppm)