Knowledge Base

Measured value relation to 35 psu

All water values given as reference values in tests or in literature are based on the assumption of a certain salt concentration. The average value of 35 psu which is usually found in natural seawater serves as a basis. This means that 35 grams of salts are dissolved in 1 liter (0,26 US.liq.gal.) of water. Learn more under  “Salinity”.

The lower the salinity of the water, the lower the concentration of all macro elements dissolved in it. For trace elements, the salt content is of less importance because their concentration will still be  sufficient for physiological processes even with lower salt density. However, the important elements such as calcium, magnesium, strontium etc. are proportionally reduced by low salt content.

An example:

Salt concentration (salinity) 30 psu – Calcium concentration 380 mg/l(0,26 US.liq.gal.) – Relational value 12.6

Salt concentration (salinity) 35 psu – Calcium concentration 440 mg/l(0,26 US.liq.gal.) – Relational value 12.6

Despite different calcium values, both relations are the same, and therefore also the low value of 30 psu is ok. The relational values at 35 psu are therefore very important to show if the measured value is tolerable according to the value relation. Otherwise it will be necessary to perform a supplementation accordingly.

The most important macro elements are summarized in a table called salinity line. This makes it quick and easy to see which water value needs to be adjusted and which ones are in the ideal range.

Functional relations

These are important relations of different water values. These measuring values show important relations. If values are set correctly, also their relation to corresponding values are within the reference range. If values show a strong shift, you need to adjust them according to the recommended values in order to fix the functional relations.

Chloride : Sulphate – relation value for determining the ion ratio

Sulphate : Sulphur – relation value for the display of sulphur compounds

Magnesium : Calcium – relation value to ensure the stability of the calcium balance

Calcium : Strontium – relative value coral growth

Potassium : Calcium – relation value coral growth, coral colour

Bromide : Fluoride – relation value inhibitors, parasite protection

Fluoride : Iodine – relation value halogens, fluorescence value, state of health

Nutrient ratio values

These are relational values of either nutrients to each other or nutrients to other types of water values. These ratios are extremely important because they have an immediate effect on health or colour and growth. If nutrient ratios are not set correctly, this has a negative effect on corals and, above all, promotes undesirable algae growth within the aquarium. In case of massive shifts you will likely face an outbreak of dinoflagellates as a result. We use exclusive ratios that have proven to be best during more than 30 years of reef aquarium maintenance, and we also use these ratios in our coral propagating systems. We do not use theoretical values from academic biology (e. g. Redfield), because they have no relevance for aquarium maintenance of corals.

Total phosphate : Nitrate = 1:100

This is about the ratio of phosphate to nitrate. You can also check this ration on your own at home in regular intervals. With this factor, the absolute measuring values are of less importance. Instead you need to keep your eye on the ration between those two values and try to maintain it on a constant level.

Important: Always try to keep the PO₄³⁻ stable and perform changes slow, ranging over several days or weeks. The nitrate value should always be higher than your PO₄³⁻ value, and in principle the nitrate value is of much less importance than the PO₄³⁻ value. Always try to work towards lower values, but keep in mind that zero values mean a nutrient limitation which would be desastrous for your corals.

Total phosphate : Iodine

We call this factor “brown level”. It describes the ratio of iodine concentration to phosphate concentration. With a low PO₄³⁻ value and a simultaneous iodine value of over 80 µg/l(0,26 US.liq.gal.), many SPS corals start to turn brownish. At the same time, however, some coral genera such as Pocillopora and Seriatopora lose brown coloration and get whitish. With this factor increasing and giving higher values, more of your corals will loose coloration and get brown. If your PO₄³⁻ value is below 0.04 mg/l(0,26 US.liq.gal.), your iodine value should not rise above 80 µg/l(0,26 US.liq.gal.).

Dynamic Elements

When studying the informations we give about the individual trace elements, you may often have seen this relation value. Dynamic Elements are those elements that unfold the most dynamics in a reef tank, and they should definitely be set correctly. In order to ensure this, the ICP analysis is a great tool. However, a measured zero value does not necessarily mean that the supply of the element in question is not sufficient: Many important elements get into the tank water during your feeding, and this has no visible effect to the ICP analysis. However, if there are visible signs of deficiency, you should adjust the values according to our recommendations.

In the measurement graphs, we give not only ideal lines but also the fluctuation ranges of the individual elements. You can see these by means of the light blue bars. As long as your measured values are within this range, the relation values are also correct, and the system is OK.

The toxicity of some elements depends on which partner elements are still present in the water. For example, a slightly increased copper concentration which would be inconspicuous with optimal relations of the other Dynamic Elements can cause poisoning symptoms in the absence of certain other elements – i.e. with shifted relations of the other Dynamic Elements. The individual consideration of an element is therefore not sufficient. Copper and other elements can be harmless even at high concentrations of more than 20 µg/l(0,26 US.liq.gal.), as long as the other dynamic elements are in a tolerable range. Other parameters also affect this, but incorrect relation values of the Dynamic Elements will certainly boost the negative effects.

Relevance values and relevance line

The relevance values don’t tell you about relations between concentrations of different elements, instead but show you at which point a certain element concentration has reached a relevant quantity. Despite the fact that several elements develop toxic properties, they may have beneficial effects on the coral physiology and might even be essential in extremely small quantities (µg/l = millionths of a gram). For certain physiological processes they are irreplaceable. However, some other elements are simply toxic and should not be detectable at all, like lead. Due to the fact that we are measuring seawater samples here, however, there is always an ICP-typical display of so-called artifacts, values that can be caused by disturbances within the measuring process.

During the last years we have worked out these values in tens of thousands of measurements and thousands of calibrations, and we have developed a system to determine these artifacts reliably. This enabled us to develop a unique method and to incorporate it into the calculations and display it in our relevance line.

The relevance line shows you the measured values in the form of a result and a graphic. As soon as they exceed the relevance line, they must be considered. Values that do not reach the relevance line can be neglected. However, keep an eye on them to see if there are any further changes.

Salinity line

The importance of salinity (salinity of the water in grams/liter (0,26 US.liq.gal.) and the optimal ratios of the macro elements to each other we have already shown in the section on salinity. In order to show this relation, we at Fauna Marin ICP Lab have developed the Salinity Line. This line shows the most important macro elements in their existing relation to salinity and shows the corresponding shifts on basis of their progression or in which range the fluctuations are appropriate for the respective elements.

You can see here at a glance which of the element needs to be corrected and in what quantity this is reasonable. On the one hand, we assume the natural conditions in seawater, but on the other hand we orientate ourselves towards the conditions in closed aquarium systems.

It does not matter what type of system you use or how you perform macro-element supplementation. The more precisely you remain into the optimal range, the more effectively your supplementation products will be used, and the less undesireable precipitations will occur. The correct setting of the salinity line is independent of nutrient concentrations or temperature.

One of the great misunderstandings in marine aquaristics is the fact that we are dealing with saltwater and therefore we want to use the corresponding tables and analyses from all parts of the world as a basis for our settings. All these analyses have been created by scientists in very complex measuring procedures. For this purpose, the water is cleaned of all foreign substances and particles, filtered, centrifuged and treated with acids.

The resulting measured values correspond to purest water from the open ocean. However, we reefkeepers use artificial salt water or at best fresh coastal seawater, which is usually always mixed with freshwater from rivers and reapective floating particles. The fact that our ICP analyses system does not find any excessive trace elements or nutrients is also due to the storage and transport time of the bottled water. For technical reasons, artificial saltwater contains many times (up to 100,000 times) more element compounds than natural seawater. Fortunately, our corals are very tolerant in this respect, but you cannot compare those two different types of saltwater. When performing an ICP analysis of aquarium water and comparing the result to natural seawater, you have to take into account those differences in order to gather values that are really relevant for a saltwater aquarium.

Carbonate-P Relation

For lovers of sensitive SPS corals like the trendy Acropora tenuis or tabulate Acropora species like Acropora hyacinthus, this relational value is an important parameter.

This relational value is about the reaction of the corals to an increased carbonate hardness with a simultaneous low nutrient level (phosphate). Corals from the outer reefs are used to very nutrient-poor water, the water is poor in particles, and the carbonate hardness is around 6.5–6.8 °dkH with a PO₄³⁻ concentration over 0.01 mg/l (0,26 US.liq.gal.).

If this relation is shifted upwards in the aquarium by the carbonate hardness, the corals die starting at the bottom. Especially Acropora tenuis suffers from a too high carbonate hardness and usually dies during about 30 days. The limiting value are 0.04 mg/l(0,26 US.liq.gal.) PO₄³⁻ and a carbonate hardness of 7.5. If the PO₄³⁻ value is higher than 0.04mg/l(0,26 US.liq.gal.), the carbonate hardness might also be slightly higher.