Coral Water Quality Guide: Ca, KH & Mg Management

Continuous water quality management is essential for coral health. Ca, KH, and Mg in particular are directly involved in calcified skeleton formation, making their maintenance the core of coral keeping.

Key Parameters and Target Values

| Parameter | Target Value | Role | |---|---|---| | Ca (Calcium) | 400-450 mg/L | Skeleton and shell formation | | KH (Carbonate Hardness) | 8-12 dKH | pH stability and skeleton formation | | Mg (Magnesium) | 1250-1350 mg/L | Maintains Ca/KH balance | | pH | 8.1-8.3 | Acid-base equilibrium | | Nitrate (NO3) | 0-10 mg/L (SPS target: below 1) | Lower is better | | Phosphate (PO4) | 0-0.05 mg/L | Lower is better |

The Relationship Between Ca, KH, and Mg

These three are closely interconnected.

• Mg plays a role in maintaining the balance between Ca and KH
• When Mg is low, Ca precipitates as lime, making it difficult to raise even with supplementation
• Managing and supplementing all three together is important

Supplementation Methods

Two-Part Solution Add Ca and KH solutions separately. Dosing pumps enable automated management. Simple and easy to implement.

Calcium Reactor Uses CO2 to dissolve coral skeleton material (aragonite) to simultaneously replenish Ca and KH. Suited for large tanks. Higher cost but excellent stability.

Three-Part Solution (e.g., Coral Snow) Separate solutions for Ca, KH, and Mg. Suited for smaller tanks.

Testing Frequency and Methods

• Weekly or more is the standard for regular testing
• Test kits: Salifert, Red Sea, and ALKAtronic are reliable and accurate
• ICP analysis: Send water samples to a lab several times a year for comprehensive analysis of 50+ elements. Also useful for trace element management

Correcting Imbalanced Values

• Low Ca: Add Ca solution in small increments. Never make large increases in a single day
• Low KH: Add KH solution (sodium bicarbonate/sodium carbonate)
• Low Mg: Replenish Mg solution (magnesium chloride/magnesium sulfate) first, then adjust others
• High nitrate/phosphate: Increase water change frequency, upgrade the skimmer, use media (biopellets, etc.)

Find Corals on Bri-Choku

In the Coral category, you'll find many corals raised under proper water quality management. Asking breeders about their water management practices can also serve as a valuable reference for your own tank.