Fritz Pro Aquatics Magnesium Chloride Flake

FritzPro Magnesium Chloride is a high-quality concentrated magnesium salt that is designed to replenish magnesium in captive reef systems.

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  • Pure magnesium chloride
  • Professional reef supplement
  • Raises magnesium in reef tanks
  • Convenient/economical high-grade bulk magnesium for experienced marine/reef aquarists
  • Use to make your own magnesium solution or dose dry
  • Ammonia- and phosphate-free

Monitoring and maintaining proper magnesium levels is an important part of stabilizing water chemistry values, resulting in better coral, coralline algae and invertebrate growth and health.

Being the third most abundant ion in natural seawater behind sodium and chloride, magnesium is an important ion for reef aquarists to understand and monitor. Magnesium is an important part of many biological processes and is an essential part of calcification. In addition to its many biological functions, magnesium helps to stabilize the correct combination of calcium, alkalinity and pH values. Severely low magnesium levels can cause low pH values and the inability to maintain proper alkalinity and calcium values. Magnesium also serves to prevent the excessive precipitation of calcium carbonate from aquarium water.

The recommended level of magnesium in the aquarium is 1250 ppm to 1350 ppm. If magnesium levels fall below this, calcium has been found to be much more difficult to get to the proper levels of concentration. Unfortunately, magnesium often is depleted from reef aquariums as calcification incorporates it into calcium carbonate skeletons and precipitates. This means magnesium concentrations that are too low can cause pumps and heaters (and any warm object) to get coated with precipitating calcium carbonate.

In full strength seawater (salinity = 35 ppt), magnesium is present between 1250 and 1350 ppm.

Magnesium helps to stabilize the correct combination of calcium, alkalinity and pH values. 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.


Add one teaspoon (3.5 g) per 10 gallons to raise magnesium by approx. 10 ppm. Dissolve the required amount in RO/DI water and slowly add to a high flow area, ideally into a sump. Re-test and repeat dose until the desired level is reached. FritzPro Magnesium Chloride can be used in conjunction with FritzPro Mag Sulfate to more closely match the natural ratio of seawater.

Usage Notes: Always test magnesium levels prior to use. Magnesium concentration found in natural seawater is between 1250-1350 ppm. Due to the sensitivity of marine organisms, it is not advisable to raise magnesium by more than 100 ppm per 24 hours.

CAUTION: This product becomes hot when mixed with water; use rubber gloves. Avoid contact with eyes, skin and clothing. Wash hands after handling.

Storage: Store in a cool, dry place with lid tightly sealed. Keep out of reach of children.

Note: Due to the variation of granular size, conversion between volume and weight of powdered products are approximate; as a precaution, dose less than the calculated amount and measure the effect before adding the total amount.