Coral Tank Calcium, KH & Magnesium Management | How to Add and Measure to Maintain Balance | ブリちょく
Coral| ✍️ BreederDirect Editorial
Coral Tank Calcium, KH & Magnesium Management | How to Add and Measure to Maintain Balance
Explains the relationship between calcium, alkalinity (KH), and magnesium—essential for coral skeleton formation—and how to add them while maintaining balance. Covers measurement frequency, how to choose supplements, and introducing calcium reactors.
Key Takeaways
Explains the relationship between calcium, alkalinity (KH), and magnesium—essential for coral skeleton formation—and how to add them while maintaining balance. Covers measurement frequency, how to choose supplements, and introducing calcium reactors.
The Three Key Elements for Coral Skeletons: The Role of Ca, KH & Mg
Coral (especially SPS and LPS) use calcium (Ca) and alkalinity (KH) in the water to build calcium carbonate skeletons. The "calcification" process is supported by the three pillars of coral tank management: calcium, alkalinity (KH), and magnesium (Mg).
Calcium (Ca): The primary building material for skeletons. Consumption increases as corals grow
Alkalinity (KH): The source of bicarbonate ions. Also contributes to pH stability. The most consumed element during coral growth
Magnesium (Mg): A "buffer" that maintains the balance between calcium and alkalinity. If deficient, precipitation of Ca and KH becomes more likely
These three elements interact with each other, so adjusting only one will not achieve stability. Managing them while maintaining balance is the key to long-term success.
Target Values and Measurement Frequency Guide
Parameter
Target
Frequency
Calcium (Ca)
380–450 ppm
Once weekly
Alkalinity (KH)
7–11 dKH
1–2 times weekly
Magnesium (Mg)
1,250–1,350 ppm
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KH fluctuates most easily, so measuring twice weekly builds confidence. If the Ca:KH ratio becomes unbalanced, precipitation can occur, so be aware of the ratio (Ca 400 ppm ≈ KH 8–9 dKH is a useful guideline).
Methods for Supplementing Calcium and KH
Two-Part Additives (Works for non-SPS too)
The simplest approach is using a two-part dosing system like Aart additives (Part 1 & 2). Calcium and alkaline components (sodium bicarbonate, etc.) are added separately.
Important: Adding both liquids simultaneously or in the same location causes precipitation. Always add them in different locations and at different times. Adding small amounts daily is ideal.
Supplementation Through Water Changes
10–15% weekly water changes using high-quality artificial seawater containing Ca and KH serve as parameter replenishment. In many cases, Ca and KH can be maintained adequately through consistent water changes alone—this is the most recommended method for beginners.
Calcium Reactor (For Advanced Users)
A calcium reactor dissolves aragonite (coral skeleton material) using CO2, then returns the reactor effluent to the tank. It's particularly effective in SPS-dominated or large-volume tanks.
Disadvantages: Complex setup and adjustment, requires pH management
Signs of Magnesium Deficiency and Correction
Typical symptoms of Mg deficiency are "parameters don't increase even when additives are added" or "white precipitate appears." Low Mg (below 1,200 ppm) promotes Ca and KH precipitation, making supplementation ineffective no matter how much is added.
To supplement Mg, use magnesium chloride (salt mag) or commercial magnesium additives. Large additions at once affect specific gravity and other parameters, so increase gradually by 50–100 ppm per day for safety.
ICP Analysis for Detailed Data
In addition to monthly test kit measurements, ICP water analysis 1–2 times yearly provides comprehensive data including trace elements (strontium, iodine, vanadium, etc.). ICP is available as an online service for a few thousand yen and can be used as a "health check" for your tank.
Summary
Coral tank Ca, KH & Mg management begins with making "measure → dose → measure" a habit. Beginners should focus on water changes; as coral numbers increase, consider introducing two-part additives or calcium reactors. Maintaining the balance of these three elements is the path to a beautiful and healthy reef tank.
