Parameter References
Reef parameters
What every number means, where it should sit, what happens when it drifts, and which test kit to actually buy. All ranges cite Randy Holmes-Farley's optimal-parameters consensus.
Alkalinity
7–11 dKHCarbonate buffer. The single most volatile reef parameter — coral reads rate of change, not absolute value.
Calcium
380–450 ppmSkeleton building block. Stable trumps high — pair every adjustment with alkalinity.
Magnesium
1,250–1,400 ppmThe reason Ca and Alk can coexist. Without it, both precipitate together.
Salinity
35 ppt / 1.0264 SG35 ppt natural seawater. Refractometer, not hydrometer.
pH
7.9–8.4An output, not a target. Driven by alkalinity and dissolved CO₂.
Nitrate
2–10 ppmEnd-product of the nitrogen cycle. Not zero — measurably low.
Phosphate
0.02–0.10 ppmCoral nutrient and algae fuel. Same molecule, two outcomes.
Temperature
76–81 °FStability over set point. 78 ±0.5 beats 76–80 swings every time.