SAK 254
What is it:
The Spectral Absorption Coefficient at 254 nm (SAK254) is an indicator for determining the concentration and nature of dissolved organic substances in water. In marine aquariums, the SAK254 value provides insight into the presence of organic compounds that absorb UV light at a wavelength of 254 nm. A high SAK254 value indicates a high concentration of these compounds, often due to biological decomposition processes.
Problems:
High organic loads in a marine aquarium generally lead to problems that negatively impact the tank. Depending on the age and condition of the aquarium, a certain amount of organic substances may be desired. However, a high concentration of these substances has effects similar to over-fertilization of plants. Organic compounds are broken down by microorganisms, leading to increased oxygen consumption. This can result in hypoxia (oxygen deficiency) in poorly circulated areas, which is particularly problematic for sensitive marine organisms such as fish and corals. The breakdown of organic substances releases nutrients like phosphates and nitrates, which can cause undesirable algae blooms in high concentrations. High organic loads can also deteriorate overall water quality by causing turbidity and releasing organic acids, which lower the water’s pH. Organic particles can clog filters and substrates, reducing the efficiency of filtration and water circulation. A high organic value can also promote the precipitation of carbonates in a marine aquarium.
Too High Value:
Use Carb L, adsorbers, light ozone application, and UV sterilizers. Water changes and switching to uncolored feed or feed with high protein and fat content are also helpful. It may also be necessary to reduce bacterial and plankton dosing.
Too Low Value:
This is a rather rare situation. In such cases, feeding the tank with coral and fish food may be helpful. Additionally, reduce skimming and the filtration through adsorbers and/or activated carbon.
| Type: | Organic |
|---|---|
| Use: | Cell functions, basic marine water element |
| Reference Range: | 0.5 – 6 m⁻¹ |
| Skill Level: | Yellow |
| Detection Quality: | Reliable |
| Relation Value: | Organic values |
| Wichtigkeit 1–6 | 2 |
| Detektionsqualität | sicher |
| Fluctuation Range: | 2–5% |
Measures:
To reduce high organic loads, use activated carbon (Carb L), UV sterilizers, ozone, and adsorbers (Phos 0.04, PowerPhos). Regular removal of sludge, maintenance and vacuuming of the substrate, and regular water changes help maintain good water quality. Also, avoid using feed with dyes. Good skimming is essential, and a light use of ozone can be helpful. However, excessive ozonation can disrupt skimming and reduce the efficiency of removing organic molecules. We recommend using 10-20 mg of ozone per 1000 liters. Note that if using ozone, it should always be filtered through activated carbon (Carb L).
What Does the SAK254 Value Measure:
The SAK 254 can be easily measured and recorded using a suitable photometer. This value is therefore well-suited for monitoring water quality in the aquarium. It can also monitor the effectiveness of filter media and the introduction of feed. Typically, there is a correlation between SAK 254 and DOC, so SAK measurements can approximate the total content of dissolved organic substances (DOC).
The SAK254 value measures the absorption of UV light by organic compounds with conjugated double bonds.
- Single Bonds (σ-Bonds):
Absorb UV light only weakly and contribute little to the SAK254 measurement. - Double Bonds (π-Bonds) and Conjugated Systems:
Absorb UV light much more strongly and are therefore mainly responsible for the SAK254 value.
The Measurement Includes:
- Humic Substances:
Complex organic substances that arise from the decomposition of organic material, also in the aquarium from the decomposition of waste, coral slime, and food residues of plant and animal origin. - Humic Acids:
Water-soluble, have high molecular weight and complex structures. These are also sometimes visible (yellowish water). When this water is exposed to UV light, a fluorescent effect can be observed with the naked eye. - Fulvic Acids:
Also water-soluble, with lower molecular weight than humic acids and characterized by long-chain and complex structures. - Humin:
Insoluble in both alkaline and acidic solutions, consisting of highly polymerized aromatic structures.
Additionally, an unknown number of various organic compounds are detected. These are collectively referred to as “yellow substances.” More information about them can be found here. There are other organic substances in the aquarium that need different methods of detection. These are also classified as yellow substances but include organic substances that do not show fluorescence or color (amino acids, phosphate compounds, terpenes, etc.).
Connection with DOC (Dissolved Organic Carbon):
The DOC value represents the total amount of dissolved organic carbon in the water. The SAK254 value is often correlated with the DOC value, as many organic compounds contain carbon and absorb UV light. However, the SAK254 value provides more specific insights into the quality and type of organic substances by focusing on UV-absorbing aromatic and conjugated compounds.
Connection with the P-Organic Factor from Fauna Marin’s Lab Measurement:
Here, we also determine the difference between total phosphate and classical ortho-phosphate as a factor value. It is assumed that the difference is organic phosphate. This method was developed by Claude Schuhmacher in 1998. You can find the guide [here](LINK to HTU).
Organic Phosphorus: Structure and Composition
Organic phosphorus occurs in many different forms, primarily embedded in organic molecules. The main classes of organic phosphorus compounds include:
- Phosphorus-containing nucleic acids
- Phospholipids
- Phosphoproteins
- Organic phosphates (e.g., phytates)
- Phosphorus-containing Nucleic Acids:
Nucleic acids such as DNA and RNA contain phosphate groups that link individual nucleotides together. The phosphate groups are present in all living organisms in aquariums, including feed, as the basis is made up of living cells. - Structure:
Phosphodiester bond (-O-PO₂-O-) links the 3′-hydroxyl group of one nucleotide to the 5′-hydroxyl group of the next nucleotide. - Composition:
C₅H₁₀O₄N₅P (example of a nucleotide)
This demonstrates that using phosphorus as a basis for measuring organic load is very sensible, as most waste products, in addition to carbon, also contain phosphorus. - Phospholipids:
Phospholipids are key components of cell membranes. They consist of a glycerol backbone, to which two fatty acid chains and a phosphate group are attached, which in turn is linked to a polar head group. These phospholipids are valuable substances, particularly in high-quality feeds such as Calanus and Mysis. The less processed the feed, the more of this valuable substance remains. - Phosphoproteins:
Phosphoproteins are proteins that contain one or more phosphate groups covalently attached to amino acid residues (often serine, threonine, or tyrosine). These substances arise from feed residues and liquid feed when combined with amino acids. - Organic Phosphates (e.g., Phytates):
Phytates are the main form of organically bound phosphorus in plants, algae, and other feed materials. They are also present in very cheap feed ingredients such as wheat gluten, algae powder, etc.
How Is the Measurement of These Substances Done?
ICP-OES and HSA for Phosphate Determination
- ICP-OES (Inductively Coupled Plasma Optical Emission Spectroscopy):
Principle: The sample is ionized in a plasma, and the emission of ionized elements is measured. The total phosphorus content is quantified through the emission of the phosphorus signal. Application: Measures total phosphorus content, including both organic and inorganic phosphates. - HSA (High-Speed Analyzer):
Principle: Specific reagents react with orthophosphate to form a colored complex that is determined photometrically.
Application: Measures only orthophosphate, which is free in the water and not bound to organic molecules.
Both laboratory devices measure phosphorus content in different ways. Comparing the two values can calculate a factor that indicates organic load. At the same time, comparing these measurements can verify the actual measurement.
- Further Development of Schuhmacher’s Organic Heat Test:
The classic heat test releases organic phosphates by heating so they can be measured as orthophosphates.
Details here
The use of ICP-OES and HSA allows for a more direct and accurate determination of total phosphorus and orthophosphate without the need for a separate heat step.
Connection to Schuhmacher’s Heat Test:
The heat test by Schuhmacher is used to determine the proportion of organically bound phosphate. This is done by comparing the total phosphate value (TP) and orthophosphate value (PO₄³⁻) before and after a heat treatment that converts organic phosphate compounds into inorganic orthophosphate.
- Total Phosphate (TP):
Total concentration of phosphate, including both organic and inorganic forms. - Ortho-Phosphate (PO₄³⁻):
Concentration of inorganic phosphate.
Connection Between SAK254 and Schuhmacher’s Heat Test:
Although the SAK254 value and Schuhmacher’s heat test measure different aspects of organic load, there is a connection between them. Organic phosphates detected in the heat test may contain aromatic structures that also influence the SAK254 value. A high organic phosphate content could therefore correlate with a higher SAK254 value if these compounds have UV-absorbing groups.
Impact of Dyes in Feed on the SAK254 Value:
- Basic Considerations:
Dyes in feed can influence the SAK254 value in a marine aquarium, as many dyes absorb UV light. This could distort the interpretation of the SAK254 value and suggest a higher concentration of organic compounds than actually present. To better understand this, we consider the chemical properties of dyes and their potential impact on the measurement value. - Impact on the SAK254 Value: Since the SAK254 value measures UV light absorption at 254 nm, dyes with UV-absorbing groups can increase the value. This leads to the following possible distortions:
- Increased Absorption: Dyes in feed can cause additional UV absorption, not originating from the usual organic compounds in the water.
- Misinterpretation of Water Quality: An increased SAK254 value could be mistakenly interpreted as a sign of increased organic load from natural organic substances (like humic substances), although it is actually caused by dyes.
Therefore, we avoid using artificial or fluorescent dyes in feed.
Direct Effects of High Organic Values:
- Acid Formation and pH Decrease:
Organic acids lower the pH and reduce carbonate concentration, affecting carbonate hardness. These organic acids are formed through the breakdown of precipitates and feed residues like detritus by the bacteria involved in the biofilm. - Nutrient Excess and Algae Growth:
Increased algae growth can cause pH fluctuations that promote carbonate precipitation. Nutrient excess also forms from the precipitation of unsuitable carbonate sources or high pH dosing systems. During precipitation, organic substances are carried away and deposited in decor or substrate. They are then processed by natural or added bacteria. - Change in Water Chemical Composition:
High organic values alter the stability of trace element composition. Especially with high phosphate levels, trace elements are difficult to keep stable. - Biofilms and Microbial Influence:
High organic loads alter the composition of microorganisms in biofilms and can cause local pH changes that promote carbonate precipitation or deposit dissolution.
Tip:
Due to the nature of the measurement, the individual components of organic load cannot be analyzed separately. We measure a total value. However, Fauna Marin provides several different values that offer a comprehensive overview of the entire organic load.
To avoid excessive organic load, only a few simple measures are needed. The choice of supply system is crucial. Additives such as bacteria, amino acids, etc., should be dosed sparingly. Always use high-quality feed with a high fat and protein content.
Continuous carbon filtration with high-quality long-term carbon (look for stick form) helps maintain organic load at a good level.
Most supply systems are designed so that initial successes are seen at the beginning of marine aquaristics. The composition with trace elements, organic acids, amino acids, dyes, and vitamins is often too high. These substances accumulate (depot effect) and can act like a gradual over-fertilization in plants. Corals react similarly, as they are naturally more adapted to limitation rather than eutrophication.