With the Salifert Profi Test Mg 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 corect calcium and alkalinity concentration difficult. The Salifert Profi Test Mg -Magnesium- can perform approx. 50 measurements in marinewater. It measures in sufficient accurate steps of 30 mg/L with a sharp color change.