Magnesium Chloride Hexahydrate - Aquariums, Deicer, Ice Melt


SKU: RD10242

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99% Technical Grade 

What is Magnesium chloride hexahydrate

Magnesium chloride hexahydrate is a naturally occurring salt with the formula MgCl2 6(H2O). It is mostly produced from sea water and in particular the Dead Sea. It is a colourless to white, odourless salt.  The main uses for magnesium chloride are in the paper, textiles, cement and refrigeration industries. It also finds major applications as a de-icer, Ice Melt and a water treatment in aquariums.

  • High quality magnesium chloride from the Dead Sea
  • Free from phosphate, bromides and ammonia
  • Dissolves quickly to provide clear solution



  • Additive for marine aquariums (see below for details)
  • Used as a deicer and Ice melt and prevents the formation of ice on surfaces
  • Used in the manufacture of textiles, fire proofing agents, cements and refrigeration bri­ne.
  • Used to make sorrel cement.
  • Used for dust control.
  • For the manufacture of magnesium metal and other magnesium compounds.

PLEASE NOTE: This product is not for human or animal consumption.



Magnesium chloride hexahydrate is for adding magnesium to sea water. Severely low values of magnesium (900 mg/L or below) can cause low pH values and an inability to maintain proper alkalinity and calcium values. If magnesium becomes too low, coral growth will stop and followed by a decline in coral health. Carbonates and calcium are essential for all growth of corals, coralline algae, clams and invertebrates. Maintaining the correct magnesium values is very important and is indirectly responsible for coral and coralline algae growth by making it possible to maintain correct calcium, alkalinity and pH values. The magnesium content must often be increased, as shortfalls in the content can arise for various reasons. The normal magnesium content is around 1.30 - 1.40 mg/litre (1300-1400 ppm). To increase the magnesium content you need magnesium chloride hexahydrate or a mixture of magnesium chloride and magnesium sulphate (ratio of 7:1).

How to dose aquarium with magnesium chloride

50g will raise Magnesium levels by approximately 60ppm in 100 litres of salt water. It is not recommended to increase Magnesium levels by more than 60ppm per day. Simply mix the required amount into a few litres of Reverse Osmosis Water, once dissolved, slowly add to your tank in an area of high flow, preferably over a period of an hour. Alternatively add to your evaporation top up water and top up as normal.

Magnesium Chloride as a de-icer / Ice melt

Magnesium chloride is considered by some to the best overall ice melting compound. It is safe to use around plant life and it is less corrosive than other ice melting compounds. Magnesium chloride is a hygroscopic compound meaning it absorbs moisture. This allows the magnesium chloride to dissolve into a brine solution very quickly hence melting ice and snow very quickly. Relatively harmless to plant life, magnesium chloride is an environmentally friendly alternative for melting ice and snow. Magnesium chloride can effectively melt ice and snow in temperatures as low as -30 degrees Celsius.

Magnesium chloride does not produce any residues that can damage carpets etc.

The product is simply applied by sprinkling the powder over the ice. When used as a solution magnesium chloride has the added advantage of preventing ice forming on surfaces when applied before freezing. This solution is made up by dissolving 30g per litre of water. It can be sprayed at a rate of approx 5 sq m per litre.


Properties of magnesium chloride hexahydrate

  • CAS No.: 7791-18-6
  • EINECS: 232-094-6
  • Formula: MgCl2 6H2O
  • Purity: 99%
  • Mol weight: 203.3
  • Density: 1.569
  • Melting point: 117C
  • Water solubility: 2350 g/L (20 C)
  • Appearance:: White flakes
  • pH: 8.4 270g/l at 20C)

Health & safety

Not a hazardous substance or mixture according to Regulation (EC) No. 1272/2008.


Click here to view MSDS

Click here to view Technical Specifications