ReMag is a new magnesium reaction media for boosting this important element from calcium reactors. Normal calcium reactor medias are basically aragonite, and primarily output calcium and carbonate and only minor traces of other elements as they are dissolved.
Two Little Fishies ReMag comes in 1 Kg and 4 Kg bag sizes since you only need a little bit of the media to compliment the normal calcium carbonate media of calcium reactors. Magnesium is an important yet essential element in reef tanks which is often overshadowed by calcium and alkalinity levels.
Having proper magnesium levels is important for skeleton-building stony corals, and also for proper chemical and biological chemistry. Having higher magnesium levels in the aquarium helps to actually get your calcium levels where they need to be. And many species of Montipora, especially encrusting species, will fail to live up to their full growth and color potential without sufficient levels of magnesium.