Introduction to Reef Tank Water Chemistry | KH・Ca・Mg Balance Management
Explaining the relationship between the three most important parameters in coral tank water quality management—KH, calcium, and magnesium. Covers how to use supplements, dosing pump settings, and water testing frequency and methods.
Key Takeaways
Explaining the relationship between the three most important parameters in coral tank water quality management—KH, calcium, and magnesium. Covers how to use supplements, dosing pump settings, and water testing frequency and methods.
Introduction to Reef Tank Water Chemistry | KH・Ca・Mg Balance Management
Reef tanks housing corals require fundamentally different water management practices compared to goldfish or tropical fish aquariums. At the core of this are three parameters: KH, calcium, and magnesium. These are deeply interconnected with one another, and if one drops out of range, the other two become unstable as well, eventually halting coral skeletal formation and potentially leading to bleaching and death. This article explains everything from the role of these three major parameters to supplement selection and daily testing habits, written in a way beginners can understand. If you'd like to review the fundamentals, see our Coral Tank Water Quality Management Guide as well.
Understanding the roles of the three major parameters
KH (Carbonate Hardness)
KH stands for "carbonate hardness" and indicates the concentration of bicarbonate ions in the water. The ideal range is 7–11 dKH.
KH's primary role is buffering pH. Acidic compounds tend to accumulate in coral tanks due to biological activity, causing pH to drop. When KH is properly maintained, it can neutralize these acids and stabilize pH. Additionally, KH is consumed when corals synthesize calcium carbonate (their skeleton).
In aquariums housing numerous SPS (small-polyp stony corals), it's not uncommon for 1–2 dKH to be consumed per day. Building a habit of checking daily is essential.
Calcium (Ca)
Calcium is the primary component of calcium carbonate (CaCO₃), which makes up coral skeletons. The ideal range is 400–450 ppm.
If levels are too low, coral growth slows and skeletons become brittle. Conversely, if too high, calcium reacts with carbonate in the water, causing "calcium precipitation" that can cause scale buildup on pipes and equipment. Since it's consumed alongside KH, if only one parameter is dropping, you'll need to adjust your supplementation balance.