Marine reef dosing

In a marine reef aquarium, hard corals (SPS and LPS) construct their skeletons by consuming calcium and carbonate ions from the water. Maintaining a stable chemical environment is critical for their survival, coloration, and growth.

The Reef Chemistry Triad

To keep a reef tank healthy, you must balance three closely related parameters:

1. Alkalinity (KH / Carbonates) (Target: 7–11 dKH): Carbonate hardness is the buffer that keeps pH stable and provides the building blocks for coral skeletons. KH is the most volatile parameter and must be kept stable.
2. Calcium ($Ca$) (Target: 380–450 ppm): The primary structural component of coral skeletons.
3. Magnesium ($Mg$) (Target: 1250–1400 ppm): Magnesium chemically binds with calcium and carbonates, preventing them from combining and precipitating out of solution (calcium carbonate precipitation). Without proper Magnesium, you cannot maintain high KH and Calcium.

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Reef Parameter Rules & Corals Impact

Use this guide to diagnose chemical imbalances in your reef:

Parameter	Deficiency Symptoms (Deficit)	Excess Symptoms
Alkalinity (KH)	Bleaching; coral tissue recession from the base (STN/RTN); skeleton growth stops.	Burnt tips on SPS corals; abiotic precipitation (white crust on heaters/pumps).
Calcium ($Ca$)	Thin, fragile coral skeletons; slowed coral growth.	Depresses Alkalinity; calcium precipitation; scaling on equipment.
Magnesium ($Mg$)	Rapid precipitation of Ca/KH; pale corals; soft corals fail to expand.	Snails and crabs become lethargic/apathetic; tissue damage in delicate corals.
Nitrate & Phosphate	Starvation: corals turn pale or white; Dinoflagellates bloom (danger to tank).	Corals turn dark brown; slowed calcification; outbreaks of hair algae/cyanobacteria.

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Reef Dosing Methods

If your corals consume more nutrients than water changes can replenish, you need to implement a dosing method:

1. 2-Part Dosing: Separately doses Calcium and Alkalinity (often with Magnesium added to the Calcium part). Dosed daily in equal amounts.
2. Balling Method: Doses Calcium Chloride, Sodium Bicarbonate, and Sodium Chloride-Free Salt. This keeps the ionic balance of the saltwater perfectly stable over time.
3. Kalkwasser (Limewater): Doses Calcium Hydroxide dissolved in freshwater (usually via auto top-off or dosing pump). It replenishes both Calcium and Alkalinity in equal parts while raising pH, but is limited by the tank’s evaporation rate.
4. Triton Method: A holistic dosing system based on regular ICP water tests, where dosing is adjusted based on trace element consumption.