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Aragonite is a form of calcium carbonate (CaCO₃)

Calcium (Ca)

Alkaline Earth Metals
Atomic Number: 20
Last Reviewed: 12/15/2024

Calcium is a vital macroelement in reef aquariums, playing a fundamental role in coral skeletal formation, shell growth, and various biological processes.

Calcium is essential for reef aquariums, as it forms the backbone of coral skeletons and other marine organisms such as clams, snails, and calcifying algae. In seawater, calcium is primarily present as free calcium ions (Ca²⁺), which are biologically available for marine life. Maintaining appropriate calcium levels is crucial for reef tank stability and coral health.

Natural Seawater Levels

Average Concentration: Natural seawater contains calcium at approximately 410–450 ppm. This range varies slightly depending on location and depth.

Optimal Aquarium Levels: Reef aquariums should maintain calcium levels within 400–450 ppm to support coral growth and stability. (NOAA)

Risks

Low Calcium (Deficiency):

  • Impaired skeletal growth in corals, clams, and calcifying algae.
  • Fragile coral structures and slowed growth rates.
  • pH instability due to insufficient buffering.

High Calcium (Excess):

  • Calcium precipitation as calcium carbonate (CaCO₃), reducing bioavailability.
  • Clogged pumps and equipment due to calcium carbonate buildup.
  • Alkalinity depletion, as excessive calcium often disrupts the calcium-carbonate balance.


Relevancy

Skeletal Growth: Corals and other calcifying organisms extract calcium and carbonate ions from the water to build their calcium carbonate skeletons.

Biological Processes: Calcium plays a role in nerve function, muscle contraction, and enzymatic activity in marine organisms.

pH Buffering: While not directly involved, calcium works in tandem with alkalinity to maintain ionic balance and stability in seawater.

Ocean Values

Reference Name Low High Optimal Unit
Hawaii Ocean 400.0000 450.0000 420.0000 mg/L
Florida Ocean 400.0000 440.0000 416.3400 mg/L
Red Sea Ocean 400.0000 450.0000 420.1200 mg/L

Regional Variations

Calcium levels in natural seawater are generally stable worldwide, with slight variations in coastal or upwelling regions.

Dosage Recommendations

Maintain calcium levels at 400–450 ppm.

Dose calcium supplements incrementally to avoid sudden changes.

Consider automated dosing systems for consistent delivery in heavily stocked tanks.

Handling

Testing: Test calcium levels weekly using a high-quality kit or digital tool.

Adjustment: Dose calcium supplements cautiously, ensuring that alkalinity and magnesium are also within optimal ranges.

Reef.Tools recommends: Maintain Calcium (Ca) concentrations between 400.0000 and 440.0000 mg/L.

References

  1. NOAA Ocean Service. "Calcium in Seawater." (NOAA)
  2. Holmes-Farley, R. "Calcium and Alkalinity in Reef Aquariums." Reefs.com. (reefs.com)
  3. Tréguer, P. J., et al. "The biogeochemical cycle of calcium in marine ecosystems." Biogeosciences, 2021. (bg.copernicus.org)

Difficulty

Rating: Moderate

Calcium management requires regular monitoring and careful dosing to maintain balance with other parameters.

Categorization

Element Type: Macroelement

Role: Coral Skeletal Growth and Ecosystem Stability

Usually Deficient

Calcium is rapidly depleted in reef aquariums due to coral calcification and other biological processes.

Essential

Calcium is critical for coral health, shell growth in invertebrates, and calcifying algae.

Aliases

Calcium Ion (Ca²⁺), Calcium Carbonate (CaCO₃), Limewater/Kalkwasser (Calcium Hydroxide)