Phosphorus / Phosphate


Phosphorus (P) or the reactive orthophosphate (PO₄³⁻) for aquaristics is the most relevant nutrient value in reef aquaria. Depending on the inhabitants, different concentrations are optimal. But the stability of this value seems to be more important that the value itself. Values between 0.02 and 0.08 mg/l (0,26 PO₄³⁻ are fine for corals.

The difference between total phosphorus (P) conveniently converted into phosphate (PO₄³⁻) and directly measured orthophosphate (like the measurement with your water test at home) defines the phosphorus deposits present in the tank water. This factor stands for your phosphate level and thus your organic depot in the reef aquarium

What’s that:

Phosphorous is the most important nutrient in a reef aquarium. In the aquarium, phosphorus is measured as orthophosphate using standard tests. This is a dissolved and reactive version of phosphorus in reef aquariums. Phosphates are largely non-toxic, but too large amounts disturb the corals. Pay attention to low and stable values around 0.02–0.08 mg/l (0,26 PO₄³⁻


Especially fluctuating PO₄³⁻ values cause problems for corals and the biological balances. Tissue detachment, algae growth, inhibited coral growth and poor coral colouration are the result of too high or too low phosphate levels. Pay attention to our nutrient recommendations for our biotopes.


Regular meadure of the PO₄³⁻ value! Adjustment the dosing and the feed input, reduce by partial water change, adsorber filtration, check the water care devices and filter media.

Indicator species:

Too high values generally show up in colour loss, browning of tissue and growth reduction. Too low values can be easily detected in Pocillopora and Seriatopora species because phosphate deficiency leads to significant brightening and the polyps remain retracted. If the values continue to sink, the corals die from the base and generally become brighter. Acropora and Montipora lose their beaming appearance and partly tan while others brighten up completely.

Value too high:

Reduce feed input, optimise skimming and filtering, clean or replace bottom substrate, use phosphate adsorber, dose bacteria and bacteria feed.

Value too low:

Dose Elementals P or Coral Balance.

Variety Nutrient
Default value 0,02–0,04 mg/l (0,26
Skill level orange
Source lining entry, decoration, plastics, frost lining, dry reef rock, activated carbon
Available Elementals P, Coral Balance, Protein Powerfood
Importance 1–6 6
Detection quality safe
Relation values Nitrate, iodine, alkalinty

Balling Light:

In the Balling Light system, no nutrient input is made in the basic supply. Calcium supply and nutrient input are strictly separated. The basic dosing via organic, and the normal feed dosing via coral and fish food is usually sufficient. Acute nutrient limitations can be balanced by Elementals P and N.

Further phosphate sources in the aquarium are solids such as precipitates, rotting corner spaces and organic compounds in the water. In our laboratory we measure both the total phosphate value (P) and the reactive phosphate (PO₄³⁻). We calculate and measure these values with a very precise method. The ratio of the two values results in an interesting measuring factor or deposit effect value. This value corresponds as a factor to the measured difference of the total phosphate and the orthophosphate. You can also perform this test at home. Please find these instructions in our download area („heat test according to Schuhmacher“).

If phosphate values are too low, you should always try to adjust the value with a suitable stocking density and balanced feeding. If this is not possible despite an adequate fish load, it can be useful to rsupplement with individual elements (Elementals P). This nutrient can also be controlled with the products Organic, Coral Balance and MIN S/ Coral Vitality.

Which one of the products is best to use and also the „when“ and „how“ should be discussed with your Fauna-Marin partner, or follow our dosage recommendations in the systems. Please note that dosaing phosphate must be done very conscientiously. It is also not necessary to achieve immediately measurable results. As a rule, a daily dosage of 0.005 – 0.01 mg/l (0,26 daily has proven to be sufficient for overcoming phosphate limitations. In this context it is also important to know that during the dosage phase it is essential to pay attention to the carbonate hardness and the calcium and potassium values.

The addition of PO₄³⁻ has a decisive influence on the bacterial activity in the aquarium and thus, in addition to the calcium values, a rapid reduction of the NO3– value can be observed. Phosphorus is also an essential nutrient in biofilms. This is stored in the EPS. If the phosphate value of the aquarium water is quickly reduced, it will quickly be increased again via an equilibrium reaction of biofilms and physical deposits. This also results in the release of further trace elements into the water. A stable phosphate value is therefore very essential because it also ensures the availability of important elements.

Phosphate and nitrogen as well as the nutrient elements are in direct relationship to each other, which is always harmoniously adjusted in best case. We can literally guarantee you a smoothly running reef tank as along as this balance is present. Our ICP Business Test demonstrates this relationship.

To illustrate this with an example: Just look at the ingredients of a normal plant fertilizer. Besides the usual elements nitrogen (N), phosphorus (P) and potassium (K), these fertilizers also contain metals such as iron, manganese or magnesium. If the corresponding ratios in the fertilizers are changed, this causes problems with plant growth and promotes weed growth, and similar effects occur with corals.


Make sure you have a nitrate/phosphate ratio of approx. 100 : 1 (i.e. 2 – 5 mg/l (0,26 NO3– to 0.02 – 0.05 mg/l (0,26 PO₄³⁻). This ratio is ideal for reef tanks.

As a rule, skimmers that are too weakly designed and and a too heavy fish load are the reason for too high nutrient concentrations in reef tanks. Always observe nitrate and phosphate simultaneously and make sure that your fish stocking density is reasonable. The commonly used systems allow for a good control. With skimmers, there are huge differences in performance. Orientate yourself on models that are used in professional breeding farms, because you won’t go wrong with those either. If you save on water current and skimming at the beginning, you will need to to dig a lot deeper into your pockets later on to get problems under control.