Dear Community,
Hardly any other water nutrient is as hotly debated in marine aquariums as phosphate (PO4). Sometimes it's demonized, sometimes it's praised as indispensable. But what's the truth? Is phosphate the enemy of our corals or a necessary building block for a healthy reef? At CommunityCorals, we want to shed light on the issue and provide you with a practical guide based on sound knowledge—including the comprehensive SANGOKAI recommendations.
What is phosphate and why is it important (or not)?
Phosphate is a chemical compound containing phosphorus—an absolutely essential element for all organisms, from the smallest bacteria to algae to our beloved corals. It is a building block for cell membranes, DNA, and important energy molecules (such as ATP).
- Sources in the aquarium: Food (fish and coral food), animal excrement, dead organisms, sometimes tap water (which is why a reverse osmosis system with a downstream ultrapure water filter is so important!), frozen food (if not rinsed) and in rare cases also certain rocks or additives.
- The problem with zu viel Phosphate: The most common consequence is unwanted algae growth. Many pest algae thrive on high phosphate levels. Another frequently discussed issue is the possible inhibition of calcification in stony corals, although the exact mechanisms are complex.
- The problem with too little Phosphate: This is where it gets exciting! An aquarium completely without detectable phosphate (“zero phosphate”) is often not The goal. Corals need phosphate to survive. A deficiency can lead to stunted growth, loss of color, tissue damage, and increased susceptibility to diseases or certain pests such as dinoflagellates or cyanobacteria. The SANGOKAI recommendations explicitly warn against such nutrient deficiencies [Source: SANGOKAI SEA-Z, e.g., pp. 99, 477, 481, 521, 716].
Measuring phosphate: knowledge is power
Regular measurements are essential. Only then will you know where your pool stands.
- Droplet tests: Cheap, but often inaccurate, especially at low ranges. Okay for a rough orientation.
- Photometer (e.g. Hanna Checker ULR): Significantly more accurate in the critical lower measurement range. A good investment for ambitious aquarists.
- Laboratory analysis (ICP-OES): The most accurate method also provides values for many other important elements. Recommended for regular, comprehensive monitoring [Source: SANGOKAI SEA-Z, p. 139ff].
What are “ideal” phosphate levels?
The short answer: It depends! an There is no perfect value. It depends heavily on the tank type and stocking:
- SPS-dominated basins: Often very low values are aimed for, typically in the range of 0,02 – 0,05 mg/L (ppm)But be careful: Too close to zero can be problematic! Experienced SPS keepers pay close attention to their corals and the nutrient balance.
- LPS and soft coral tanks: These often tolerate and require slightly higher values, e.g. 0,05 – 0,1 mg/L (ppm) or sometimes even slightly higher. Here, the nutrition of the corals is often more important.
- Beginners/Mixed Pools: A good starting area is often 0,04 – 0,08 mg/L (ppm)More important than an exact value is the stability and avoiding extreme lows or highs.
Important note: Don't just look at phosphate! The ratio to nitrogen (measured as nitrate) also plays a role (keyword: N:P ratio). An imbalance can also contribute to problems.
Managing Phosphate: The Reef Aquarist's Toolbox
1. If phosphate is too high:
- Cause research: Is the fish intake too high? Are you feeding too much or the wrong food? Is the osmosis system working correctly? Are you rinsing frozen food? This is eternity the first step!
- Phosphate adsorber:
- Function: They chemically bind phosphate (and often silicate) to their surface. Commonly used granules are iron-based (GFO) or aluminum-based. [Source: SANGOKAI SEA-Z, p. 74, 1101]
- Application: Best used in a fluidized-bed filter for maximum efficiency, but also possible in a filter bag (move regularly!). Start slowly to avoid dropping the filter reading too quickly!
- Advantages: Very effective.
- Disadvantages: They can reduce phosphate levels too much (risk of deficiency!), materials must be replaced (ongoing costs), and some products can release metals into the water (pay attention to quality!). SANGOKAI refers to them as "anion adsorbers." [Source: SANGOKAI SEA-Z, p. 72, 1084, 1988]
- For the budget-conscious: Adsorbent bags are cheaper than reactors, but less efficient. Large containers are often more cost-effective.
- Algae refuge / compensation biotope:
- Function: Fast-growing macroalgae (e.g. wire algae – Chaetomorpha) consume nutrients such as phosphate and nitrate for their growth. Regular harvesting of the algae permanently removes the nutrients from the system. [Source: SANGOKAI SEA-Z, pp. 100, 102, 1481]
- Advantages: Natural method, stabilizes the system, provides habitat for microorganisms.
- Disadvantages: Requires space, light, and current. Can compete with corals in the main tank if nutrient deficiencies occur. Must be well cared for (regular harvesting!). [Source: SANGOKAI SEA-Z, pp. 111-112, 1488, 1514-1520, 1535]
- water change:
- Function: Dilutes all substances in water, including phosphate.
- Advantages: Easy to do, brings fresh trace elements (if good salt is used).
- Disadvantages: Often very inefficient at high levels. For example, to reduce 50 mg/L of nitrate (a similar principle applies to PO4) by half, several consecutive changes are required at 20% water content. This costs money (salt, water). [Source: SANGOKAI SEA-Z, pp. 154ff, 2463-2485]
- Protein skimmer: Primarily removes organic compounds before they are broken down into inorganic phosphate. Thus, it helps indirectly, but hardly removes bound phosphate. [Source: SANGOKAI SEA-Z, pp. 55, 788, 990]
- (Biopellets & Co): Methods such as biopellets bind nutrients in bacterial biomass. This must then be removed by the skimmer. SANGOKAI advises against using biopellets because of the risk of nutrient re-dissolution and sludge formation if the chain is not functioning perfectly. [Source: SANGOKAI SEA-Z, pp. 38, 70, 1035, 1049-1083]
2. If phosphate is too low:
- More feeding: Feed the fish and corals selectively (high-quality food!). Increase slowly and monitor values.
- Dosing phosphate: There are special solutions or powders for targeted increases. Dose very carefully and measure daily! Small steps are key here.
- Reduce exports: Remove or reduce the adsorber quantity, shorten the lighting duration in the refugium, and adjust the skimmer to a drier setting. [Source: SANGOKAI SEA-Z, p. 729 (implied for skimmer), pp. 111-112 (refuge)]
Conclusion for the CommunityCorals family
Phosphate is not an enemy, but a vital partner in the complex ecosystem of our reef aquarium. As is often the case in marine aquariums, it is about BALANCENeither too much nor too little is good.
- For beginners: Don't panic! Measure regularly (a Hanna Checker is a good investment), keep the values stable within a moderate range (e.g., 0,04-0,08 mg/L), and focus on the basics: good water quality (osmosis!), proper feeding, and a good skimmer. If you're using adsorbers, start slowly!
- For the thrifty person: Source control is the most cost-effective method! Algae refugia can be inexpensive with a little DIY skill. Use adsorbent bags and replace smaller amounts more frequently.
- For the PLC professional: You know the drill. Fine-tuning colors and growth, keeping an eye on the danger of zero levels, managing nutrient ratios, and using ICP analyses for control.
The most important thing is to observe your tank closely. What do the corals look like? Are there any algae problems? React slowly and carefully to changes in water parameters.
We hope this guide helps you better understand the topic of phosphate and maintain your reef even more successfully!
Feel free to share your experiences and questions in the comments!
