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How to read the results of your ICP-OES water test from "The ICP lab"

By Gene Diveglia



While we will be the first to admit that we love to dive deep into the details of ICP-OES analysis of seawater just for fun, we don’t lose sight of the fact that ICP-OES testing is an important part of reaching your reefing goals and a valuable tool for solving problems both large and small. ICP-OES testing produces a wealth of technical data for each sample tested. What you see in your test results is a tiny fraction of the data produced by each test. Much of this data is technical in nature and requires some transformation so that it is useful for anyone, regardless of background.


The biochemistry that occurs in a closed aquaculture system is anything but simple. Regardless of whether we, as hobbyists or aquaculture professionals, understand this chemistry, it is still present, and it is the engine of the aquatic lifeforms that we all love so much.

Biological and metabolic processes in reef systems rely upon specific ranges of concentration of a variety of elements. These concentrations range from macro elements present in parts per thousand through minor and trace elements that reach down to the low parts per billion. A few trace elements are active and beneficial even in the high parts per trillion. Some of the least concentrated trace elements, such as Iron, Zinc, Selenium, and Vanadium, are essential for the organisms present in our reef systems. Even though these elements are only present in the parts-per-billion or less, life ceases to exist without them.

Regardless of your choice of method to maintain the vitality of your reef system, none of these essential elements will drop to zero concentration. Such absolutes are unattainable outside of a laboratory environment, as even the air contains minute confrontations of these elements in the low parts per trillion. However, that doesn’t mean we should ignore the maintenance of trace elements in a reef system. While corals, bacteria, and other organisms may be able to survive at ultra-low concentrations of these elements, survival is not the same thing as thriving. Careful maintenance of trace and minor elements in beneficial ranges will bring you closer to a thriving reef system than no maintenance at all.


The first thing to realize when you view your test results report is that a concentration of ’not detected’ for any element on your report doesn’t mean this element is completely absent from your sample. It just means it is below the detection limit of the test. Fortunately, optimum levels of the beneficial minor and trace elements tested in the ICP-OES report are all within the measurable range of the test. So ’not detected’ for a beneficial element just means you need to supplement it. For contaminants a concentration of ‘not detected’ is optimal.

Similarly, macro, minor, and trace elements highlighted in light blue are deficient and should be supplemented to achieve the best coloration, health, and growth of corals, as well as optimum nutrient removal from bacterial processes. There are many products available to repair elemental deficiencies. However, it is also essential to keep in mind that when you add an element into your system, you are also potentially adding other elements or even contaminants that may not be clearly labeled on the product. We recommend using trace element additives from Captiv8 Aquaculture* because they are of high purity and clearly describe what they contain.

The second thing to know is that any element highlighted in yellow is elevated beyond the range that we consider to be optimal. This doesn’t mean you need to take immediate action. It just means you should watch how the concentration of this element changes on your next test. Is it continuing to elevate? Or is it returning to its normal range?

The third thing to understand is that the elements highlighted in red need immediate attention. These elements are far enough out of range that you do need to take action to avoid a likely problem. Depending upon how far out of range the element is, which element it is, and how long it has been elevated will determine how high the risk is and how imminent it is. Likewise, different species exhibit different degrees of response to elevated elements. So, it's best to address these as soon as possible to minimize the risk of a costly problem. For example, elevated levels of Zinc or Nickel will cause slow tissue necrosis in many species of Acropora. Similarly, elevated levels of Manganese can cause rapid tissue necrosis in some of the more sensitive Acropora species. Removal of elevated elements or contaminants isn’t always as simple as solving deficiencies. Provided that a high-quality salt blend is being used, water changes will always dilute and reduce the presence of contaminants or elements that are elevated. Depending upon the concentration of the elevated element, more aggressive water changes may be necessary, up to 30% per change every other day for several days. GFO, activated carbon, resins, and similar products can also be very effective depending upon the element or contaminant that needs to be removed. Your test results will identify which methods are effective for any elevated elements present in your sample.

The last major point to understand is the value of monitoring trends. Each element on the report shows how it has changed from the previous test. Additionally, each element tab can be expanded to show additional information about the importance of the element, the recommended ranges, and the detection limits. This information is very helpful in understanding how your elemental concentrations are changing over time and helps you to solve problems before they occur.

There is much more valuable information in the report, but the points above are the foundation. As a side note, some of you have asked how we have determined the optimum ranges of concentrations we recommend in our reports. There are a wide variety of opinions regarding the optimal elemental concentrations for seawater. Many of these opinions have come from many decades of ocean water studies and can be found in numerous published papers. Much of this information was gathered over a span of time that included significant developments in available tools and techniques. Given the many challenges present in accurately measuring the concentration of trace elements in seawater, this is often a major contributor to discrepancies and differences between published papers. Other factors include where the water samples were obtained. We have tested many ocean water samples that demonstrate significant variations due to geological variations as well as other factors. Lastly, the hobby industry has a long history of fostering a multitude of opinions regarding the value or lack of value of many elements. Many of these opinions resulted from a period of time marked by a lack of available remedies or a discovery process dominated by trial and error. However, our recommendations are based on a critical analysis of published papers employing modern analytical techniques and thousands of tests we’ve performed, extensively backed by direct observations of the health and vitality of the systems tested. Our recommended ranges are generally more aggressive compared to the industry average because our goal is to help you to achieve the results we all want: thriving corals. Our recommended ranges are safe while remaining as effective as possible.


Trace and minor elements affect species and even subspecies of corals in different ways that are far from being even partially understood and cataloged. These elements are vital in metabolism, immune system function, growth, and coloration. For example, many species of Goniopora respond very well to Vanadium and Manganese concentrations in the low ppb by exhibiting better growth, polyp extension, and even improved coloration in some cases. However, there are other species of Goniopora that don’t respond at all. Trace elements are also an essential part of the epigenetic factors that can influence gene expression in corals. This is an even less understood area of coral biology that is only beginning to be explored and documented.


Fortunately, we don’t need to understand the precise mechanisms at work to take advantage of the substantial benefits of optimizing macro, minor, and trace elements in our reef systems. The availability of high-quality elemental supplements combined with precise, accurate, and reliable ICP-OES testing from Reef Labs puts exceptional results within the reach of any hobbyist.


We hope this article is valuable and helpful in turning your ICP-OES report into an action plan to advance your reef system closer to reaching your goals. As always, we would love to receive your feedback to help us continue improving the usability and value of our test results.



*Reef Labs, Inc. does not receive commission or any remuneration from Captiv8 Aquaculture for referrals. Captiv8 Aquaculture is one of our industry collaborators with whom we share a commitment to facts and integrity.

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