Seachem - Reef Advantage Magnesium
Reef Advantage Magnesium is a concentrated (80,000 ppm) optimized blend of magnesium, chloride, and sulfate salts designed to restore depleted levels of magnesium with minimal impact to the ionic ratios found in natural sea water.
Reef Advantage Magnesium contains no ammonia. This is a common contaminant in every liquid magnesium supplement on the market.
Severely depleted levels of magnesium (below 800 mg/L) can cause depressed pH levels and an inability to maintain proper magnesium levels. The most frequent causes of magnesium deficiency are use of kalkwasser, frequent overdosing of a carbonate additive, or low levels in the salt mix itself. Kalkwasser, for instance, precipitates magnesium as magnesium hydroxide while excess carbonates precipitate it as magnesium carbonate. In both cases, this means that magnesium that was present in the water is now unavailable. Of the two, magnesium hydroxide and magnesium carbonate, the former is more problematic; it is extremely insoluble.
Once magnesium has precipitated as magnesium hydroxide, it will never redissolve. Magnesium carbonate will redissolve; however, it does so slowly. So, while it will go back into solution, there will be a significant portion of time in which magnesium levels are depleted.