With the Salifert Magnesium test kit you can determine the Magnesium content in seawater exactly and easily. Calcium and strontium will not interfere the test, when their total concentration is between 300 and 500 mg/l. This is mostly the case. Natural sea water has a magnesium concentration of approx. 1300 - 1500 mg/l. The concentration varies with salinity. Too low magnesium concentration makes maintaining correct calcium and alkalinity concentration difficult. Can perform approx. 50 measurements in marine water. It measures in sufficient accurate steps of 30 mg/L with a sharp color change.