Potassium is one of the key elements for successful reef aquaristics. Since it must be available in a suitable proportion at all times, it is also one of these important elements. 

Potassium is a macro element with importance for skeletal growth and cell function as well as nutrient conversion, but at the same time also a “fertilizer” for zooxanthellae. It is therefore important to keep the potassium value as stable as possible. 

It is therefore contained in seawater in a comparable quantity to calcium, and it is no less important. The correct concentration in relation to the other macro elements is important for the successful aquarium care of corals. If you maintain a reef tank with mixed coral inhabitants and you use a high-quality brand salt mix to perform regular partial water changes of 10 percent per week, a potassium deficiency will very likely not appear.

What is this:
Potassium is a macro element that should always be set slightly below the calcium value (Ca value minus 20 mg/l). The optimum value is between 380 and 420 mg/l. Potassium is a nutrient and part of the supply process for corals and biofilms.     
Too low or too high potassium values disturb the nutrient turnover in the aquarium and have basically damaging influence on the coral growth as well as the colour formation. 
Regular control of the potassium value, observance of the salinity line, partial water change with Fauna Marin Professional Sea Salt as well as dosing via Elementals K. Due to the strongly varying consumption of the systems, individual dosing is advisable. The potassium value can be tested at home with the Aquahome Test K. 
Indicator species:
The best indicator corals for potassium concentration are Acropora valida and the red Montipora with foliate growth. Acropora valida shows bright tissue and bright violet growth tips only if the potassium value is correct. The red Montipora quickly becomes pale with potassium deficiency and stops growing, recognizable by the lack of white growth margins.

Value too high:

reduce dosage, filter via zeolite, perform partial water changes

Too low Value:

Dose Elementals K 

Type metal, nutrient salt
Standard value 380-420 mg/l
Skill Level orange, for experts only
Source salt mix, supply systems, trace element concentrates, potassium additives
Available Elementals K
Importance 1–6 5
Detection quality reliable
Relation value Calcium

Balling Light:

Supplementation of potassium is always subject to the individual consumption of the respective aquarium system. For this reason, Balling Light only contains a basic dosage. Once an additional consumption and the necessary supplementation have been determined, it can be applied regularly using the product Elementals K. Elementals K cannot be added to canister 1 “Calcium”.

Potassium is needed for many supply processes in corals. Among other things, potassium is a transport element for certain tunnel proteins and is involved in the formation of chromoproteins. The zooxanthellae also need potassium because it plays a role in the synthesis of glucose in photosynthesis. In addition, potassium is required in biofilm metabolism as well as in many enzymatic reactions. Potassium is also incorporated into the coral skeleton.

The consumption of potassium is system-dependent; consumption can be higher when zeolites are used or additional bacterial cultures or artificial decorations are used. Potassium should therefore be measured and added regularly. The optimum value is between 400 and 420 mg/l. A reduction of 5 percent can already have an effect on the growth and colouring of corals. Potassium is not part of the Balling-Light system due to its strongly system-dependent consumption. You should always add potassium individually and adjust the dosage quantities. This is particularly important when using zeolites or ceramic decorations.

Most aquarium enthusiasts still assume that the brightening of corals is mainly caused by nutrient limitations. As a rule, however, the reason is that the potassium concentration is too low and simultaneously the nutrient values have shifted. The relations have been altered, and as a result the corals fail to maintain several important biological processes with the consequence of brightening tissues.  

Potassium deficiency has a particular effect on the fast-growing Montipora and Seriatopora species. The growth will slow down or stop completely, the colour appears grey and bland or washed out, in Seriatopora corals the tissue dissolve under these conditions starting at the bottom. This effect will be increased with alkalinity increased above 8 °dKH. In general, a potassium deficiency is noticeable in slowed growth and poor nutrient conversion, and it can also be responsible for excessive nutrient levels. 

In general pale colours and a greying of the colours can be observed, tissue detachment in the shaded areas takes place as well as sudden tissue dissolving in Euphyllia species and other corals. Here, special attention should be paid to the PO4 value, because with a lower PO4 value the corals’ reaction to a potassium deficiency will be more extreme. 

Potassium can be increased to values of up to 700 mg without negative effects on corals (unlike shrimp, see below). Some SPS hard corals show burnt growth tips when the iodine concentration is too low. Too high potassium values lead to spotty tissue in some corals with partially small detachments. However, these too high potassium values do not lead to a detachment of the tissue from below! In general, however, in this case you find a clearly visible darkening of the corals and slowing down of growth. 

Shrimps react the fastest with a too high potassium value and can suffer damages already starting from approx. 500 mg/l or perish. Therefore, keep the potassium value stable. You can measure the potassium value at the aquarium very precisely with the Fauna Marin Aquahome Test. 


Pay attention to the total amount of potassium brought in. The natural values of at least 380 mg/l should always be achieved in the sea salt used. Trace element concentrates do contain potassium, but at too small concentrations to have a relevant effect on the potassium supply of the aquarium. An example would be iodine preparations containing potassium iodide. As the amount of iodine here is about 10,000 times less than the amount of potassium introduced, no effective potassium supplementation is possible by adding a trace element solution.