Coral Essentials - Part C Magnesium is a concentrated source of liquid magnesium, 12,500 ppm (mg/L). Coral take up magnesium into their calcium carbonate skeletons. It is important to maintain adequate magnesium levels as this is essential in maintaining correct calcium and alkalinity levels. Poor magnesium levels usually result in the need for addition of much higher levels of calcium and carbonate than would normally be required. It serves to prevent the excessive precipitation of calcium carbonate from aquarium water. The magnesium levels in marine tanks need to be checked regularly to determine the take up in your system. Magnesium usage can be calculated by testing at regular intervals to see how much the level drops.  Then it is simple to calculate dosing requirements to suit the depletion rate. After you have determined this, a regular check of the magnesium levels should be made. Your tank will change over time as coral grows, new pieces are added as well as most other aquarium inhabitants also take up magnesium. We have found ideal magnesium levels to be at about 1350-1400ppm for most aquariums.