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For biologically ideal magnesium intake in the reef aquarium




Product description

Besides calcium and strontium, some coral and coralline red algae also store magnesium in their skeleton. It is biochemically directly involved in the photosynthesis of algae, i.e. the conversion of carbon dioxide and light into organic compounds. Magnesium is therefore one of the most important minerals of seawater.


Tropic Marin® Bio-Magnesium provides magnesium and carbon dioxide in a biologically optimally usable form, preventing magnesium deficiency in seawater and restoring the natural concentration ratio of the alkaline earth metals. These are basic requirements for a healthy coral reef in the aquarium.



  • For biologically ideal magnesium supply in crystalline form in the reef aquarium

  • Provides magnesium for strong skeletal growth of coral and coralline red  algae

  • Provides carbon dioxide for the zooxanthellae to support photosynthesis and calcification  

  • The natural ionic composition and the pH of the water are not changed

  • Without unnatural by-products

  • Without phosphates and nitrates

  • Exact dosing and easy application


magnesium salts, sodium and potassium as well as 70 trace elements

Application & Dosage

Natural seawater has an average magnesium content of 1280–1300 mg/l. First, measure the magnesium concentration of your aquarium water and estimate the water volume of your tank system, taking into account the decoration (stones, etc.).



The addition of one measuring spoon of Tropic Marin® Bio-Magnesium increases the magnesium content by about 10 mg/l per 100 l (26 gallons) of water.

Maximum recommended dose: 2 measuring spoons per 100 litres (26 gallons) of aquarium system water volume per day.


To use, fill the dosing spoon with Tropic Marin® Bio-Magnesium and level using scraper. Distribute the contents of the measuring spoon well by stirring at the surface of the water. Make sure that no larger undissolved Tropic Marin® Bio-Magnesium crystals come into direct contact with the corals. Add the next spoon when the previous one has dissolved.


The addition of ½ fl.oz./15 ml will raise the magnesium level of 10 US-gal./38 l by approx. 21 mg/l (ppm).

Maximum recommended dose: ½ fl.oz./15 ml per 10 USgal./38 l of aquarium water per day.

Tropic Marin® Bio-Magnesium Liquid can be added to the tank water either directly or by a dosing pump.

To refill the bottle you can fill up 16 oz./450 g crystalline Tropic Marin® Bio-Magnesium with reverse osmosis water to 0.26 US-gal./1 liter solution.

Concentrations of more than 1600 mg/l magnesium should be avoided, as various organisms may react negatively to extremely high magnesium levels.

Over time, the specific gravity of the water can increase slightly. Please check the specific gravity regularly. Besides the magnesium concentration, the calcium content should also be monitored. Use the Tropic Marin® Calcium/ Magnesium-Combitest Professional for monitoring these levels, and the Tropic Marin® Carbo-Calcium and Tropic Marin® Bio-Magnesium to adjust them when needed.

Dosing calculator


Other product recommendations

Besides checking the density, the magnesium concentration and the calcium content should also be observed. The Tropic Marin® Calcium/Magnesium-Combitest Professional is best suited for this. As a calcium source we recommend Tropic Marin® Carbocalcium.



Frequently asked questions

Answers to frequently asked questions about this product can be found in our FAQ section.

Container sizes

Tropic Marin® Bio-Magnesium:                                                                      Tropic Marin® Bio-Magnesium Liquid:
450 g / 15.8 oz.                               Art. Nr. 29402                                           1000 ml / 33.8 fl.oz.                       Art. Nr. 29454
1500 g / 52 oz.                                Art. Nr. 29432


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