Magnesium (Mg)
Alkaline Earth Metals
Atomic Number: 12
Last Reviewed: 12/15/2024
Magnesium is a critical macroelement in seawater, essential for maintaining the chemical stability of reef aquariums. It plays a central role in maintaining calcium and alkalinity levels, supporting coral health, and preventing undesirable chemical precipitation. Magnesium is often referred to as the "glue" that binds calcium and carbonate ions in solution, allowing corals to utilize them for skeletal growth.
Natural Seawater Levels
Concentration: Magnesium in natural seawater is typically around 1,280–1,350 mg/L. This range provides a stable environment for marine life and supports the ionic balance.
Risks
Deficiency:
- Leads to instability in calcium and alkalinity levels, as calcium carbonate becomes more prone to precipitation.
- Corals may exhibit slowed growth rates, weakened skeletons, and reduced coloration due to poor calcium uptake.
- Photosynthetic efficiency in macroalgae and symbiotic dinoflagellates may decline.
Excess:
- Elevated magnesium levels (above ~1,500 mg/L) may lead to chemical imbalances and stress on invertebrates.
- Excessive magnesium can potentially interfere with other trace elements, such as strontium and potassium, disrupting ionic balance.
Relevancy
Buffering Role: Magnesium prevents calcium carbonate from precipitating by interfering with the crystallization process, maintaining calcium and carbonate in solution.
Coral Skeletal Growth: Coral skeletons primarily consist of aragonite (a form of calcium carbonate). Magnesium indirectly supports this process by stabilizing calcium levels.
Photosynthesis: Magnesium is a component of chlorophyll, crucial for photosynthetic organisms like zooxanthellae, which reside in coral tissues.
Ocean Values
| Reference Name | Low | High | Optimal | Unit |
|---|---|---|---|---|
| Florida Ocean | 1200.0000 | 1400.0000 | 1300.0000 | mg/L |
| Caribbean Ocean | 1250.0000 | 1300.0000 | 1280.0000 | mg/L |
| Australia Ocean(Generic) | 1250.0000 | 1300.0000 | 1280.0000 | mg/L |
Regional Variations
Magnesium concentrations in seawater are consistent across ocean basins, with slight variations in salinity due to regional freshwater inputs or evaporation.
Dosage Recommendations
Target Level: Maintain magnesium levels between 1,280–1,350 mg/L.
Adjustment: Dose magnesium supplements incrementally, using a mix of magnesium chloride and sulfate.
Handling
Testing: Use reliable test kits or ICP-OES for accurate measurement.
Storage: Store magnesium supplements in a dry, cool place to prevent caking or contamination.
Reef.Tools recommends: Maintain Magnesium (Mg) concentrations between 1300.0000 and 1400.0000 mg/L.
References
- Bruland, K. W., & Lohan, M. C. (2003). "Controls of Trace Metals in Seawater." The Oceans and Marine Geochemistry. (Oxford Academic)
- Millero, F. J. et al. (2008). "Thermodynamics of Seawater: A Global View." Ocean Science Journal. (Journals.Ametsoc.org)
- Treguer, P. J., et al. (2014). "The Biogeochemical Cycle of Magnesium in the Ocean." Biogeosciences Discussions.
Difficulty
Rating: Easy
Magnesium levels are relatively stable in most aquariums due to its abundance in seawater and salt mixes. However, monitoring and adjustments require attention to avoid imbalances.
Categorization
Element Type: Macroelement
Role: Chemical Stability, Coral Skeletal Growth
Usually Deficient
Heavy coral growth or calcification can deplete magnesium over time. Low-quality salt mixes or inadequate water changes may lead to deficiencies.
Essential
Magnesium is necessary to prevent calcium carbonate precipitation and ensure the bioavailability of calcium and carbonate for coral growth.
Aliases
Mg, Magnesium Chloride (MgCl₂), Magnesium Sulfate (MgSO₄)
