Jump to this value
Physical-chemical basic values
Macro elements, calcium balance elements, and halogens
Relational values of macro elements and halogens
Macronutrients
Nitrate/PO4 PO4/Iodine PO4/Carbonate Hardness
Metabolically relevant micronutrients, color-relevant trace elements
Additional trace elements, possible pollutants
Further information
Physical-chemical basic values
50.9 mS/cm 25°C
What is it: This is about the salt content in seawater. Many major components only undergo minor changes worldwide. Salt content, nutrient concentrations, and external inputs are the main variables.
Problems: Too high or too low salt concentrations lead to problems in many aquarium animals. Reduced growth, pale colors, and lack of or reduced polyp extension are early signs. The conductivity of aquarium water should always be adjusted to 49 – 53 mS/cm.
Measures: Regularly check salt content, top up with osmosis water, or refill with seawater to compensate for losses due to skimmers, etc.
What to do here
1.0221 kg/L 25°C
What is it: This is about the salt content in seawater. Many major components only undergo minor changes worldwide. Salt content, nutrient concentrations, and external inputs are the main variables.
Problems: Too high or too low salt concentrations lead to problems in many aquarium animals. Reduced growth, pale colors, and lack of or reduced polyp extension are early signs. The density of aquarium water should always be adjusted to 1.021 – 1.023 kg/l.
Measures: Regularly check salt content, top up with osmosis water, or refill with seawater to compensate for losses due to skimmers, etc.
What to do here
33.375 psu
What is it: This is about the salt content in seawater. Many major components only undergo minor changes worldwide. Salt content, nutrient concentrations, and external inputs are the main variables.
Problems: Too high or too low salt concentrations lead to problems in many aquarium animals. Reduced growth, pale colors, and lack of or reduced polyp extension are early signs. The salinity of aquarium water should always be adjusted to 32-35 PSU.
Measures: Regularly check salt content, top up with osmosis water, or refill with seawater to compensate for losses due to skimmers, etc.
What to do here
7.89
What is it: The pH value indicates whether water is acidic or basic. Seawater is slightly basic, with a pH of 7.9 to 8.3.
Problems: Too low or too high pH values affect many biological processes in the aquarium. Low pH levels can cause phosphate and trace element deposits to dissolve from rock decorations, while high pH levels can cause precipitations. This can lead to fluctuations in nutrient concentrations, algae and cyanobacteria growth, and dinoflagellate blooms. A stable pH value is therefore crucial. A daily fluctuation of up to 0.3 units is normal.
Measures: We recommend regular pH monitoring and implementing the following measures to avoid strong pH fluctuations:
- Regular partial water changes
- Check skimmer efficiency
- Ensure adequate room ventilation
- Maintain sufficient flow in the aquarium
- Monitor and regulate nutrient concentrations
- Check and balance trace element concentrations using Tropic Marin® Components or Block solutions
- Regularly clean or replace substrate
- Reduce short-chain organic carbon dosing
- Use Tropic Marin® Nitribiotic
What to do here
8.7 °dKH
What is it: Carbonate hardness (°dKH), technically measured as acid capacity of water to pH 4.3, is a sum parameter of different pH buffer systems. Since it mainly reflects the concentration of bicarbonate and carbonate ions, KH is very important for reef aquariums. An alkalinity test (“carbonate hardness test,” e.g., KH Pro) should be part of the basic equipment. While carbonate hardness and acid capacity are technically different, we use the common term carbonate hardness for easier understanding. Together with calcium and magnesium concentration, carbonate hardness determines the calcium supply in reef aquariums.
Problems: Too high or too low carbonate hardness is directly related to calcium and magnesium, as well as phosphate consumption in fast-growing small-polyp stony corals. A stable buffer system in seawater requires sufficient bicarbonate and carbonate ions. Corals react quickly to low levels, and even more so to high levels, by reducing polyp extension, experiencing tissue loss at the base, and slowing growth.
Measures: Regular carbonate hardness measurement and dosing are essential for maintaining a successful reef aquarium. The carbonate hardness should be maintained between 6.0 – 8.0 °dKH. In justified cases, deviations may be acceptable.
What to do here
3.25 mg/l
What it is: CO2 is a gas called carbon dioxide. Part of this gas turns into carbonic acid H2CO3 in water, which acidifies the water accordingly. CO2 is produced as a waste product during respiration, formed by bacteria, and enters or escapes the water through the skimmer and water surface.
Problems: Excessively high CO2 levels indicate an excessive input of CO2 into the water but can also signal high nutrient concentrations or a disturbance in the buffering system. This results in impaired coral growth and the release of phosphates and trace elements from storage. Increased algae growth and unsightly coatings may follow.
Measures: Regular monitoring of pH value, sufficient water flow and aeration. Observe carbonate additions.
What to do here
3.1059 mmol/L
What it is: Carbonate hardness (°dKH), technically measured as the water's acid capacity down to pH 4.3, is a sum parameter of various pH buffering systems. Since it mainly reflects the concentration of bicarbonate and carbonate ions, KH is very important in reef aquariums. An alkalinity test ("carbonate hardness test," e.g., KH Pro) should be part of the basic equipment. Although carbonate hardness and acid capacity are technically different, we use the common term "carbonate hardness" for easier understanding. The supply of calcium in the reef aquarium depends on carbonate hardness, calcium, and magnesium concentrations.
Problems: Too high or too low carbonate hardness interacts directly with calcium and magnesium (the calcifying elements) and with the nutrient phosphate, which is increasingly consumed by rapidly growing small-polyp stony corals due to calcification. A stable buffering system in seawater requires sufficient amounts of bicarbonate and carbonate ions. Corals respond quickly to low and especially to high levels with reduced polyp extension, tissue recession at the base, and reduced growth.
Measures: Regular measurement and dosing of carbonate hardness are essential for successful reef aquarium care. Carbonate hardness should be in the range of 6.0–8.0 °dKH. In justified individual cases, deviations may occur.
What to do here
What it is: "Yellow substances" refer to a mixture of long-chain organic decomposition and condensation products that give the water a yellowish or brownish tint. These can enter the water through food or as bacterial decomposition products.
Problems: Reduction and color shift of coral lighting, especially filtering out the blue spectrum. Binding of trace elements and nutrients.
Measures: Yellow substances can be removed from aquarium water using activated carbon, aluminum-based phosphate adsorbers, ozone, and UV sterilizers. Regular use of Tropic Marin® Carbon or Tropic Marin® Cyo-Control helps control yellow substances. Caution is advised during application, as a sudden increase in the blue light spectrum may harm corals.
Learn more...What it is: Odors can have various causes. Dead fish, stressed or dying corals or other animals, leftover frozen food, infestations with dinoflagellates or algae, and even ozone can be sources of odors in the aquarium room or at the aquarium itself. If an unusual smell is noticeable, the cause should be investigated.
Problems: Decaying areas or dead animals in the aquarium promote rapid bacterial growth. Rotting zones can release toxins into the water, especially if sediment or substrate is stirred up.
Measures: Odors can be removed from aquariums with Tropic Marin® Carbon, Tropic Marin® Elimi-Phos, ozone, and a well-tuned skimmer. Regular use of Tropic Marin® Carbon or Tropic Marin® Cyo-Control helps keep the water fresh and clear.
Learn more...Macro elements, calcium balance elements, and halogens
18474.4 mg/l
What it is: Chloride is the dominant ion in our sea salt. Together with sodium, it forms sodium chloride. Chlorides are salts of hydrochloric acid and can combine with many other metals, e.g., calcium (calcium chloride), magnesium (magnesium chloride), and many others.
Problems: Too high or too low salt concentrations cause issues for many aquarium animals. Reduced growth, pale colors, and poor or absent polyp extension are early signs. The aquarium water conductivity should always be maintained between 49–53 mS/cm.
Measures: Regular monitoring of salinity, topping off with reverse osmosis water or seawater to compensate for losses (e.g., through skimming).
What to do here
10736 mg/l
What it is: Sodium is the dominant metal ion in our sea salt. Together with chloride, sodium forms table salt, the base of sea salt.
Problems: Too high or too low salt concentrations cause issues for many aquarium animals. Reduced growth, pale colors, and poor or absent polyp extension are early signs. The aquarium water conductivity should always be maintained between 49–53 mS/cm.
Measures: Regular monitoring of salinity, topping off with reverse osmosis water or seawater to compensate for losses (e.g., through skimming).
What to do here
821 mg/l
What it is: Sulfur, in the form of sulfate ions, is another dominant element in seawater. A few amino acids and other compounds contain sulfur, but the quantities bound in this way are low. While sulfate itself is harmless at normal concentrations, it can be reduced to highly toxic hydrogen sulfide through decay processes. This hydrogen sulfide is oxidized into sulfur by sulfur bacteria at the transition between the oxygen-poor decay zone and oxygen-rich water. White, mold-like coatings from sulfur bacteria are an indication of hydrogen sulfide.
Problems: Elevated or reduced sulfate concentrations should be avoided. Deviations can be corrected by partial water changes. If the variation exceeds 30%, laboratory verification is recommended. Low sulfate levels may contribute to coral weakening.
Measures: Regular monitoring of sulfur and sulfate concentrations, regular partial water changes with Tropic Marin® Sea Salt. To increase magnesium levels, magnesium sulfate or Epsom salt should never be used alone.
What to do here
2459.716 mg/l
What it is: Sulfur, in the form of sulfate ions, is another dominant element in seawater. A few amino acids and other compounds contain sulfur, but the quantities bound in this way are low. While sulfate itself is harmless at normal concentrations, it can be reduced to highly toxic hydrogen sulfide through decay processes. This hydrogen sulfide is oxidized into sulfur by sulfur bacteria at the transition between the oxygen-poor decay zone and oxygen-rich water. White, mold-like coatings from sulfur bacteria are an indication of hydrogen sulfide.
Problems: Elevated or reduced sulfate concentrations should be avoided. Deviations can be corrected by partial water changes. If the variation exceeds 30%, laboratory verification is recommended. Low sulfate levels may contribute to coral weakening.
Measures: Regular monitoring of sulfur and sulfate concentrations, regular partial water changes with Tropic Marin® Sea Salt. To increase magnesium levels, magnesium sulfate or Epsom salt should never be used alone.
What to do here
417 mg/l
What it is: Potassium is a macro element that should be present at slightly lower levels than calcium. The optimal range is between 380 and 420 mg/l. Potassium is a nutrient and important for ion balance.
Problems: Too low or too high potassium levels disrupt ion balance in the aquarium and negatively affect coral growth and coloration.
Measures: Regular monitoring of potassium levels, observe the salinity line, perform partial water changes using Tropic Marin sea salts, and dose using Components Potassium. As potassium is consumed at different rates in different aquariums, we recommend individual dosing based on verified demand. Potassium levels can be determined using the Potassium Test Professional.
What to do here
4.19 mg/l
What it is: Boron occurs in seawater as boric acid and borate anions, depending on pH. This is the basis for its pH-buffering effect, contributing a few percent to KH. At 4–6 mg/l, it is still considered a macro element despite its low concentration. Boron is essential, particularly for cell membrane growth and stability. High boron levels reduce the harmful effects of elevated aluminum concentrations.
Problems: Low boron levels inhibit coral growth. Levels below 2 mg/l may cause blister-like tissue detachment.
Measures: Regular monitoring and adjustment of boron concentration. Reduce boron levels through partial water changes and dosage adjustment.
What to do here
1371 mg/l
What it is: Magnesium is an important macro element that contributes to salinity. Magnesium forms ion pairs with carbonate without precipitating, stabilizing the calcium content in the water. As a minor component in calcium skeletons, its consumption and required dosing are significantly lower than calcium. Red algae in particular consume more magnesium than stony corals, due to the type of calcium they form. Coral skeletons (aragonite) absorb little magnesium, while magnesium calcite in red algae absorbs more.
Magnesium is also related to phosphate and its consumption, as it is directly involved in energy and phosphate metabolism.
Problems: Magnesium levels up to around 1,600 mg/l are acceptable. Higher values cause chemical imbalance with calcium, possibly resulting in tissue deterioration in soft corals and tissue detachment in SPS corals. Some sources recommend levels above 1,800 mg/l to combat algae, which we strongly advise against.
Low levels below 1,100 mg/l increase the risk of precipitation with rising KH and calcium levels. The link to energy and phosphate metabolism may explain coral bleaching and tissue detachment in LPS corals from the base upward.
Measures: Regular monitoring of magnesium levels, maintain ion balance, lower high magnesium levels through partial water changes with Tropic Marin® Classic, and dose with Tropic Marin® Components Magnesium.
What to do here
465 mg/l
What it is: Calcium is a main component of all calcium skeletons and must therefore be regularly monitored and supplemented in reef aquariums. In these skeletons, calcium combines with carbonate to form solid, water-insoluble calcium carbonate. Coral skeletons, clam shells, and red algae structures are made of different types of calcium minerals.
Problems: Low calcium levels can lead to increased KH and reduced growth. Extremely low levels below 300 mg/l may cause slimy tissue breakdown. High calcium levels tend to lower KH.
Measures: Regular calcium level monitoring. When adjusting calcium, consider the ratio to magnesium. Regulate the calcium-to-KH ratio using Tropic Marin® Original Balling Part A or Part B or Tropic Marin® Components Calcium or Carbonate.
What to do here
7.24 mg/l
What it is: As an alkaline earth metal, strontium behaves similarly to calcium. It appears to play an important role in skeletal growth. No known positive metabolic functions are attributed to strontium. Ideal concentrations are between 7–10 mg/l.
Problems: Low strontium levels reduce growth in stony corals and red algae. High levels make coral skeletons brittle and soft; growth tips crumble with pressure or touch.
Measures: Regular monitoring and appropriate dosing of strontium, partial water changes with Tropic Marin® sea salts, dosing with Tropic Marin® Components Strontium and Tropic Marin® Block Strontium. Strontium should be dosed in a fixed ratio to calcium. Strontium is the key element in the Tropic Marin® Block Strontium solution.
What to do here
78.3 mg/l
What it is: Bromine is a halogen and, with approximately 67 mg/l of bromide, a macro element in seawater. Biologically, bromine is mainly incorporated into the defense compounds of algae and other marine organisms. Similar to iodine, it also contributes to the strengthening and hardening of organic skeletons, such as those of gorgonians, sponges, and crustaceans.
Problems: Low bromine concentrations impair the growth and coloration of horn corals, sponges, soft, and stony corals. High concentrations above 90 mg/l can harm corals.
Measures: Regular monitoring of bromide concentration, adjust dosing if necessary, lower through partial water changes and use of Tropic Marin® Carbon.
What to do here
0.59 mg/l
What it is: Fluorine is present in seawater as fluoride. This element cannot be measured via ICP analysis and must be determined separately using IC/HPLC. Fluoride is essential for corals. In addition to its inhibitory effect on bacteria and algae, it is important for coral growth and defense against parasites. It also influences the blue coloration of many corals.
Problems: Too little fluoride results in dull tissue, reduced growth, colorless growth tips or edges in foliaceous corals (e.g., Montipora species), and increased light sensitivity. Corals also become more susceptible to parasitic infections. The skeleton becomes noticeably softer.
Measures: Regular monitoring of fluoride levels and dose adjustment if needed. Reduce through partial water changes and adjusting dosing.
What to do here
0.018 mg/l
What it is: Iodine holds special importance in reef aquariums. Inorganic iodine occurs mainly as iodate and to a lesser extent as iodide in seawater. Near the surface, iodate is reduced to iodide by microalgae, creating a near-surface maximum of iodide.
Problems: Low iodine levels are first noticeable in gorgonians: the polyps no longer open or open incompletely, growth slows, and coloration fades. With further declines, soft and stony corals are also affected. Stony corals exhibit problems adapting to changing light conditions and become light-sensitive when iodine is deficient.
Measures: Regular monitoring of iodine concentration and dose adjustment if necessary. Lower iodine levels through partial water changes and adjusting dosage. Iodine is the key element in the Tropic Marin® Block Iodine solution.
What to do here
Relational values of macro elements and halogens
0.954
What it is: This refers to the ratio of salinity to the calculated target value.
1.2
What it is: This refers to the ratio of carbonate hardness to the calculated target value.
41.079
What it is: This refers to the ratio of magnesium content to the measured salinity.
13.933
What it is: This refers to the ratio of calcium content to the measured salinity.
0.217
What it is: This refers to the ratio of strontium content to the measured salinity.
12.49
What it is: This refers to the ratio of potassium content to the measured salinity.
0.126
What it is: This refers to the ratio of boron content to the measured salinity.
553.541
What it is: This refers to the ratio of chloride content to the measured salinity.
73.7
What it is: This refers to the ratio of sulfate content to the measured salinity.
7.511
What it is: This relation indicates a potential ion imbalance.
Measure: Adjust the target values of the individual elements as instructed.
2.996
What it is: This relation shows an important factor in the sulfate system. Verifying a value using two different measurement methods ensures measurement quality.
Measure: If the deviation from the target value is too large, please seek advice.
2.948
What it is: This relation shows the correct ratio between two key calcium-related values. This is a particularly important relation.
Measure: Adjust the target values of the individual elements as instructed.
64.227
What it is: This relation is especially important for coral growth. Calcium and strontium should always be in a fixed ratio. If the ratio deviates too much, coral growth stops—even if the individual values seem fine.
Measure: Adjust the target values of the individual elements as instructed.
132.712
What it is: This halogen ratio is important for fluorescence development and coral health. Imbalances often lead to unwanted algae growth and tissue darkening.
Measure: Adjust the target values of the individual elements as instructed.
32.24
What it is: This halogen ratio is important for coral health, growth, and skeletal hardness. Imbalances of these elements, especially when combined with nutrient shifts, often trigger unwanted dinoflagellate infestations.
Measure: Adjust the target values of the individual elements as instructed.
Macronutrients
0.09 mg/l
What it is: Nitrite appears as an intermediate in nitrification and denitrification. Due to the high chloride concentrations in seawater, nitrite uptake is inhibited, which means elevated nitrite levels are often observed in marine aquariums.
Problems: Unlike in freshwater, nitrite is not toxic in seawater. However, the accumulation of nitrite and nitrate can lead to undesirable algae growth in aquariums.
Measures: If values are too high, dosing bacteria like Tropic Marin® Nitribiotic is recommended. Phosphate and trace elements like zinc help reduce excess nitrite and nitrate. The aquarium should be checked for dying organisms, and fish feeding should be reviewed and adjusted if necessary.
What to do here
14.84 mg/l
What is it: Corals are adapted to nutrient-poor conditions and can therefore utilize different nitrogen forms such as ammonium and nitrate. Corals and microalgae prefer ammonium, as the uptake rates are higher at low concentrations, and nitrate processing stops entirely when sufficient ammonium is available. At low ammonium and phosphate levels, nitrate can harm corals, causing the sunlit areas of stony corals to "burn."
Fixed nutrient ratios in the aquarium are not significant because different nutrients have different uptake rates at various concentrations. Corals have a lower nitrogen demand than algae. At low nitrogen availability, corals have an advantage over algae. With phosphate, it is usually the opposite.
Problems: Nitrate is rather problematic as a nutrient. The concentrations at which nitrate is discussed are significantly higher than the level useful as a nutrient. Effects that occur only above 2.5 mg/l nitrate are not nutrient-related but are likely due to its oxidizing properties.
Measures: Regular monitoring of nitrate concentration provides good insight into the nitrogen balance. Regulation of nitrate is not directly necessary; phosphate concentration control is more useful.
What to do here
0.032 mg/l
What is it: Phosphorus is the most important nutrient in a reef aquarium. In the aquarium, phosphorus is measured as orthophosphate using commercial tests. This is a dissolved and reactive form of phosphorus in reef aquariums. Phosphates are largely non-toxic, but excessive concentrations cause disturbances in coral skeletal density. Stable values should be maintained, ideally around 0.1 mg/l.
Problems: Fluctuating and decreasing PO43- values cause problems with coral growth and survival. Detachments, algae growth, coral growth stops, and poor coloration are usually the results of too low phosphate concentrations. See our information on nutrient dosing, which often considers phosphate concentration as a core parameter.
Measures: Regular monitoring of PO43- values! Adjust dosing and food input, reduce through trace element dosing, partial water changes, organic carbon dosing, or phosphate adsorbers, check equipment and filter media.
What to do here
0.09811 mg/l
What is it: Phosphorus is the most important nutrient in a reef aquarium. In the aquarium, phosphorus is measured as orthophosphate using commercial tests. This is a dissolved and reactive form of phosphorus in reef aquariums. Phosphates are largely non-toxic, but excessive concentrations cause disturbances in coral skeletal density. Stable values should be maintained, ideally around 0.1 mg/l.
Problems: Fluctuating and decreasing PO43- values cause problems with coral growth and survival. Detachments, algae growth, coral growth stops, and poor coloration are usually the results of too low phosphate concentrations. See our information on nutrient dosing, which often considers phosphate concentration as a core parameter.
Measures: Regular monitoring of PO43- values! Adjust dosing and food input, reduce through trace element dosing, partial water changes, organic carbon dosing, or phosphate adsorbers, check equipment and filter media.
What to do here
0.076 mg/l
What is it: Phosphorus is the most important nutrient in a reef aquarium. In the aquarium, phosphorus is measured as orthophosphate using commercial tests. This is a dissolved and reactive form of phosphorus in reef aquariums. Phosphates are largely non-toxic, but excessive concentrations cause disturbances in coral skeletal density. Stable values should be maintained, ideally around 0.1 mg/l.
Problems: Fluctuating and decreasing PO43- values cause problems with coral growth and survival. Detachments, algae growth, coral growth stops, and poor coloration are usually the results of too low phosphate concentrations. See our information on nutrient dosing, which often considers phosphate concentration as a core parameter.
Measures: Regular monitoring of PO43- values! Adjust dosing and food input, reduce through trace element dosing, partial water changes, organic carbon dosing, or phosphate adsorbers, check equipment and filter media.
What to do here
0.114 mg/l
What is it: Silicates are salts of silicic acid. Together with feldspars and quartz, they make up a significant part of the Earth's crust and enter bodies of water as dissolved silicic acid through weathering. In aquariums, high silicic acid concentrations lead to excessive diatom growth, a problem that mainly occurs during the startup phase.
Problems: Excessive silicic acid concentrations promote diatom blooms, while low concentrations tend to favor green algae. Many sponges require some silicic acid in the water for good growth.
Measures: Water treatment via reverse osmosis with a downstream mixed-bed resin filter.
What to do here
0.244 mg/l
What is it: Silicates are salts of silicic acid. Together with feldspars and quartz, they make up a significant part of the Earth's crust and enter bodies of water as dissolved silicic acid through weathering. In aquariums, high silicic acid concentrations lead to excessive diatom growth, a problem that mainly occurs during the startup phase.
Problems: Excessive silicic acid concentrations promote diatom blooms, while low concentrations tend to favor green algae. Many sponges require some silicic acid in the water for good growth.
Measures: Water treatment via reverse osmosis with a downstream mixed-bed resin filter.
What to do here
151.255708
What is it: Since nutrient uptake by corals occurs separately for each nutrient (e.g., ammonium, nitrate, and phosphate) and at different rates, fixed nutrient ratios can only be established for specific concentrations. We recommend a phosphate concentration of around 0.1 mg/l for good coral coloration and growth. When dosing nutrients with Tropic Marin® Plus-NP, nitrogen and phosphorus are dosed at a molar ratio of 7:1.
Problems: If nutrients are supplied in unfavorable ratios, a nutrient deficiency may occur under certain conditions. It has been observed that phosphate is a particularly critical nutrient, and phosphate deficiency can quickly lead to damage or the death of corals. Elevated nitrogen concentrations, in combination with other critical algae nutrients, can cause corals to darken and turn brown, as well as promote algae growth problems.
Measures: The high phosphate demand of corals for growth, skeletal formation, and good coloration is addressed through a molar nitrogen-to-phosphorus ratio of 7:1 in Tropic Marin® NP-Bacto-Balance and Tropic Marin® Plus-NP.
5.3613
What is it: Increased iodine concentrations combined with very low phosphate concentrations can cause corals to turn brown. To avoid coral browning, we recommend phosphate concentrations above 0.05 mg/l, ideally between 0.1 and 0.15 mg/l.
Problems: If iodine concentrations exceed 80 µg/l, special care should be taken to ensure that phosphate concentration does not drop below 0.05 mg/l. Contrary to a still widely held belief, increased phosphate concentration does not cause corals to darken or turn brown.
Measures: Ensure that phosphate concentration does not fall below 0.05 mg/l.
0.0113
What is it: This ratio is particularly important for keeping Acropora species and SPS corals, as well as other stony corals. In natural seawater worldwide, at a salinity of 35 PSU, carbonate hardness is about 6.5°dH, with a low PO43- content of 0.01-0.02 mg/l. In addition to dissolved reactive phosphate, corals also have access to other dissolved and particulate phosphates. The significance of phosphate particles, e.g., from fish feces, has been largely underestimated.
Problems: Acropora species, other small-polyp stony corals (SPS), and corals in general react to increased KH with stress symptoms, such as retracted polyps and poor polyp extension (from 8° KH) and, at even higher levels, tissue necrosis starting from the base (STN, slow tissue necrosis). These symptoms occur particularly when phosphate concentrations are below 0.05 mg/l.
Measures: Corals tolerate increased KH above 7.5° KH poorly, especially at low phosphate concentrations. For optimal growth, phosphate concentration and KH must be balanced.
Metabolically relevant micronutrients, color-relevant trace elements
3.9 µg/l
What is it: Zinc plays a central role in enzymes in all living organisms. Examples include carbonic anhydrase, which is involved in bicarbonate conversion in numerous metabolic pathways, and alkaline phosphatase, which is involved in phosphate uptake and utilization.
Problems: If zinc concentrations are too low, nutrient utilization and skeletal growth are impaired. Zinc is generally necessary for calcium carbonate formation and respiration.
Measures: Zinc concentration can be adjusted through trace element dosing and partial water changes. Excess zinc can be reduced using phosphate adsorbers such as Tropic Marin® Elimi-Phos and Tropic Marin® Elimi-Phos Longlife.
What to do here
5.1 µg/l
What is it: Vanadium has regulatory functions, activates certain enzymes, and is found in high concentrations in sea squirts. Some of its functions, such as those in sea squirts, remain unexplored.
Problems: Optimal vanadium concentrations enhance coral coloration and fluorescence.
Measures: Excess vanadium concentrations can be reduced through partial water changes and phosphate adsorbers. At low concentrations, vanadium should be dosed using Tropic Marin® Components Vanadium, Tropic Marin® Block Molybdenum, or Tropic Marin® A- Elements.
What to do here
0.62 µg/l
What is it: Copper is an important essential trace element in seawater. The concentration of bioavailable copper is tightly regulated by organisms, including cyanobacteria. For corals, copper is essential for regulating the redox balance.
Problems: Low copper concentrations are important for the redox balance and coloration of corals. However, excessive copper concentrations lead to coral bleaching, first noticeable in Acropora species. Since copper binds significantly to organic particles and biofilms, shellfish and snails, which filter these particles or graze on biofilms, are affected first.
Measures: Partial water changes, filtration using phosphate adsorbers such as Tropic Marin® Elimi-Phos or Tropic Marin® Elimi-Phos Longlife, and eliminating the source of contamination.
What to do here
7.5 µg/l
What is it: Nickel is a component of enzymes that play a crucial role in nitrogen uptake and calcium carbonate formation. Nickel promotes coral growth and enhances darker, deeper coloration by supporting nitrogen metabolism and skeletal formation.
Problems: High nickel concentrations lighten corals by displacing iron. Corals bleach and exhibit very poor growth.
Measures: Filtration using phosphate adsorbers such as Tropic Marin® Elimi-Phos Longlife or Tropic Marin® Carbon (activated carbon).
What to do here
0.2 µg/l
What is it: Manganese is present in seawater at very low concentrations. The distribution of its highly variable concentrations shows a maximum at the ocean surface, influenced by airborne dust deposition. Manganese is an essential element involved in photosynthesis and detoxification of reactive oxygen species. Corals require more manganese than iron for their metabolic processes.
Problems: Low manganese concentrations negatively affect photosynthesis and the detoxification of reactive oxygen species. Manganese deficiency leads to reduced growth and retracted polyps as protection against oxidative stress, especially in Goniopora and Alveopora species. The production of reactive oxygen species makes corals more light-sensitive.
Measures: Removal through phosphate adsorbers such as Tropic Marin® Elimi-Phos Longlife. However, manganese precipitates quickly, often alongside other trace elements such as cobalt and copper. Dosing through partial water changes or trace element supplementation.
What to do here
7.8 µg/l
What is it: Molybdenum exists in reef aquariums under pH values and redox potentials as an anion, like vanadate, in the form of molybdate. Molybdate is relatively soluble and long-lasting under reef aquarium conditions, so consumption and supplementation are minimal. Molybdenum is an essential trace element for most living organisms. It is primarily found in enzymes involved in nitrogen metabolism. In bacteria, molybdenum also plays a role in the enzyme formate dehydrogenase.
Problems: As photosynthetic organisms due to their zooxanthellae, corals have an intense and branched nitrogen metabolism and therefore depend heavily on an adequate supply of molybdenum.
Measures: Molybdenum is only slowly degraded in reef aquariums. Water changes, filtration using Tropic Marin® Carbon (activated carbon), and phosphate adsorbers like Tropic Marin® Elimi-Phos help reduce its concentration.
What to do here
Iron
Not detectable
What is it: Iron is an important essential trace element and is one of the few "control elements" in reef aquariums that can significantly promote the growth of algae and cyanobacteria.
Problems: Iron is necessary for chlorophyll synthesis and catalyzes numerous oxygen-related reactions in enzymes. It is best known for oxygen transport through the red blood pigment hemoglobin. However, iron is a particularly dual-natured element, as it quickly reaches concentrations where oxidation becomes harmful or even destructive. Low iron concentrations enhance the fluorescence colors of corals, particularly the green fluorescence color, which serves both as light protection and protection against oxygen radicals. Higher iron concentrations can damage corals, leading to dull, bleached colors. Due to their different biochemical composition, nuisance algae and cyanobacteria particularly benefit from higher iron concentrations, gaining an advantage over corals under such conditions.
Measures: Biopolymers, such as those found in Tropic Marin® Reef Actif, help regulate iron levels. By binding to phosphate, iron phosphates precipitate. However, since iron also precipitates very quickly, it remains an important component of trace element supplementation.
What to do here
2 µg/l
What is it: Chromium is an essential trace element involved in carbohydrate and fat metabolism. However, as Chromium(VI) in the form of chromate, it is toxic. Therefore, only Cr(III) is considered as a trace element.
Problems: Chromium as Chromium(III) is not very toxic in marine aquariums since Chromium(III) hydroxide has very low solubility.
Measures: Chromium in the form of chromate can primarily enter reef aquariums through Portland cement and cement-based mortars.
What to do here
Cobalt
Not detectable
What is it: Cobalt is an ultra-trace element in seawater and is present only in the smallest concentrations, which is why it is often not detected in ICP analysis. Additionally, it binds easily and precipitates, for example, with manganese oxides. As an essential trace element, it is found in vitamin B12, which can only be synthesized by microorganisms. Many algae rely on a supply of vitamin B12 and therefore depend on symbiosis with microorganisms. In fish, vitamin B12 is produced by microorganisms in the gut.
Problems: Reduced growth and poor coloration due to cobalt deficiency.
Measures: Optimal cobalt concentrations improve growth and color development.
What to do here
Additional trace elements, possible pollutants
205 µg/l
What is it: Lithium is an alkali metal and has become well known for its use as the third-lightest element in energy storage. Its natural concentration in seawater is 180 µg/l. If lithium exceeds 500 µg/l, corrective measures should be taken. Since alkali metal ions like lithium generally cannot be significantly reduced through adsorption or precipitation, partial water changes are the most effective solution.
Problems: None
Measures: Adjust dosage to match natural concentrations.
What to do here
19.4 µg/l
What is it: Barium, like magnesium, calcium, and strontium, is an alkaline earth metal. The carbonates and sulfates of barium are insoluble in water. The precipitation as sulfate limits barium concentration. Barium is absorbed and accumulated by ornamental algae, a family of green algae, and deposited as barite. The barite crystals in ornamental algae may serve as gravity sensors. Barium occurs in seawater at a concentration of 15 µg/l.
Problems: Barium is incorporated into calcium structures, particularly aragonite, similar to strontium. Since it is permanently removed from the water in this process, supplementation up to the natural concentration is recommended.
Measures: Barium is reduced through calcium deposition and precipitation. As an immediate measure, partial water changes are suitable.
What to do here
31.1 µg/l
What is it: Aluminum is the third most abundant element on Earth and the most common metal (element), particularly in the form of feldspars and clay minerals.
Problems: Aluminum hydroxide binds phosphate, which is utilized in aluminum-based phosphate adsorbers. Elevated aluminum concentrations in water can occur with excessive use of phosphate adsorbers. The use of such phosphate adsorbers may cause issues for corals, particularly leading to the deterioration of soft corals from the base upwards.
Measures: Monitor aluminum concentration via ICP analysis, eliminate aluminum sources if necessary, especially phosphate adsorbers, cement mortar, and ceramics, and perform partial water changes.
What to do here
Antimony
Not detectable
What is it: Antimony is a toxic metalloid.
Problems: Sources of antimony contamination include plastic components and possibly also feed.
Measures: Elevated antimony concentrations can be reduced through partial water changes and iron-based phosphate adsorbers such as Tropic Marin® Elimi-Phos Longlife. The source of the increased antimony concentration should be identified and eliminated.
What to do here
Tin
Not detectable
What is it: The highest tin concentrations in the ocean are found near the surface, reaching up to 3 µg/l. Although tin is not highly toxic, concentrations in reef aquariums should not exceed 10 µg/l.
Problems: Tin concentrations above the recommended limit can lead to slow tissue degradation in SPS corals. Natural seawater can become contaminated with tin during transport in metal tanks. Improper processing of float glass in new aquariums and catalysts used in plastic polymerization for polyurethane (adhesives) can contribute to elevated tin levels. Some frozen feeds may also contain tin.
Measures: Filtration using an iron-based phosphate adsorber such as Tropic Marin® Elimi-Phos Longlife, partial water changes.
What to do here
Beryllium
Not detectable
What is it: Beryllium is a toxic alkaline earth metal and should not be detected in ICP analysis. Contamination may come from frozen feed.
What to do here
Selenium
Not detectable
What is it: Selenium occurs in seawater at a concentration of 0.16 µg/l. It is related to sulfur and is an essential trace element. Selenium is required in enzymes for detoxification and neutralization of oxygen radicals, protecting lipid membranes in cells from oxidation.
Problems: Too low selenium concentrations can cause light sensitivity in corals. Selenium deficiency in fish leads to liver damage. Excess selenium levels in the µg/l range should be avoided.
Measures: Partial water changes or supplementation with trace element solutions.
What to do here
Silver
Not detectable
What is it: Colloidal silver is an old bactericidal agent that has recently been used in clothing and as a treatment against cyanobacteria.
Problems: Colloidal silver should never be used against cyanobacteria, as it non-specifically affects other bacteria as well. In an environment significantly shaped by microorganisms, bactericidal agents should not be used.
Measures: Due to the high chloride ion concentration, dissolved silver quickly precipitates in marine aquariums.
What to do here
Tungsten
Not detectable
What is it: Occurs in extremely low concentrations in seawater, at only 10 ng/kg, and is not detected by ICP analysis. Tungsten has a biological function in some microbial enzymes, such as bacterial formate dehydrogenase, where it serves the same function as molybdenum in other bacteria.
Problems: Tungsten should not be detected in marine aquariums. Positive results should be verified.
Measures: Check pumps for steel shafts. Perform partial water changes.
What to do here
Lanthanum
Not detectable
What is it: Lanthanum is a transition metal used in reef aquariums to effectively reduce phosphate concentrations. In marine aquariums, lanthanum rapidly precipitates as lanthanum phosphate and lanthanum carbonate. The lanthanum-containing particles should be filtered out of the water as quickly as possible.
Problems: Lanthanum should be dosed very conservatively and, if necessary, repeated until a phosphate level of approximately 0.2 to 0.4 mg/l is reached. The precipitated products should be removed from the water as quickly as possible using a skimmer and/or filtration. Excess concentrations of these particles can damage fish gills, with tangs being particularly sensitive. Flatworms are killed by lanthanum, which should be considered when using liquid phosphate removers. Toxic species such as Convolutriloba should be removed as thoroughly as possible beforehand. The precipitation of lanthanum carbonate can slightly lower carbonate hardness. Manufacturer dosing recommendations should be strictly followed.
Measures: Monitor and discontinue the dosing of liquid phosphate removers. Lanthanum is quickly removed from the water cycle through precipitation.
What to do here
Titanium
Not detectable
What is it: Titanium occurs in extremely low concentrations in seawater, approximately 7 ng/kg, which is below the detection limit of ICP analysis. Titanium metal and titanium alloys are sometimes used in reef aquariums, for example, for pump shafts, and are suitable for seawater. Titanium dioxide is a commonly used pigment, formerly also as a food coloring, and could potentially find its way into reef aquariums. Measuring titanium in seawater is associated with uncertainties due to the seawater matrix.
Problems: None
Measures: Detection of titanium in seawater should be verified.
What to do here
Scandium
Not measured!
What is it: Scandium is a rare light metal naturally present in seawater at concentrations below 1 ng/kg. It has no biological significance. It should not be detected in reef aquariums.
Zirconium
Not detectable
What is it: Zirconium occurs in seawater at a concentration of 14 ng/kg and should not be detected by ICP analysis. Zirconium has no biological function.
What to do here
Arsenic
Not detectable
What is it: Arsenic is a toxic metalloid that occurs in seawater at a concentration of 1.5 µg/kg. Arsenic has recently been classified as a biological trace element and may be enriched in frozen feed. Artificial ceramic decorations may also contribute to increased arsenic concentrations. Elevated concentrations above 5 µg/l should not be present in reef aquariums. Phosphate adsorbers such as Tropic Marin® Elimi-Phos and Tropic Marin® Elimi-Phos Longlife effectively remove arsenic.
Problems: Arsenic is sometimes detected in ICP analyses. Action is required at levels around 10 µg/l, which is also the drinking water limit.
Measures: Arsenic, like phosphate, is effectively adsorbed and removed by phosphate adsorbers such as Tropic Marin® Elimi-Phos Longlife.
What to do here
Cadmium
Not detectable
What is it: Cadmium is a highly toxic metal found in seawater at a concentration of 70 ng/kg (0.07 µg/kg).
Problems: Cadmium should not be detected in ICP analysis.
Measures: Partial water changes. Cadmium adsorbs to various adsorbent materials and phosphates. Identify and eliminate the source.