Water chemistry
Water chemistry
Convert GH and KH, calculate dissolved CO2, plan RO/tap water mixing, and correct marine salinity.
GH hardness conversion
Convert general hardness between German degrees, French degrees, ppm, and mmol/L.
Results
Formula
1 dGH = 1.786 fH = 17.848 ppm CaCO3 = 0.1783 mmol/L
KH / TAC conversion
Convert carbonate alkalinity between German degrees, French degrees, ppm, and meq/L.
Results
Formula
1 dKH = 1.786 fH = 17.848 ppm CaCO3 = 0.3566 meq/L
Dissolved CO₂ calculator
Estimate CO₂ concentration in mg/L from pH and KH using the Henderson-Hasselbalch equation.
Results
Quick pH / KH / CO2 table
| KH / pH | 6.0 | 6.4 | 6.6 | 6.8 | 7.0 | 7.2 | 7.4 | 7.6 |
|---|---|---|---|---|---|---|---|---|
| 2 | 60 | 24 | 15 | 10 | 6 | 4 | 2 | 2 |
| 4 | 120 | 48 | 30 | 19 | 12 | 8 | 5 | 3 |
| 6 | 180 | 72 | 45 | 29 | 18 | 11 | 7 | 5 |
| 8 | 240 | 96 | 60 | 38 | 24 | 15 | 10 | 6 |
| 10 | 300 | 119 | 75 | 48 | 30 | 19 | 12 | 8 |
| 12 | 360 | 143 | 90 | 57 | 36 | 23 | 14 | 9 |
| 15 | 450 | 179 | 113 | 71 | 45 | 28 | 18 | 11 |
The pH/KH CO2 calculation is useful as an estimate, but acidifiers, peat, tannins, or non-carbonate buffers can distort it.
Formula
CO₂ = 3.0 × KH × 10^(7.00 - pH)
Water mixing
Calculate the mixing ratio of RO/tap water to reach target hardness.
Results
Formula
C₁V₁ + C₂V₂ = Cₜ(V₁ + V₂)
Density & salinity (marine)
Convert between density, specific gravity, salinity (ppt), and conductivity for marine aquariums.
Results
The gram correction assumes roughly 1 g/L per 1 ppt: always dissolve salt separately and verify with a calibrated refractometer.
Hardness, CO2, and salinity calculators
This page combines GH and KH conversions, CO2 estimation, RO/tap water mixing, and marine salinity. It is designed for preparing water changes, correcting values, and reading tests without manual steps.
Scientific references
- Henderson-Hasselbalch equation
- Carbonate buffer system CO₂/HCO₃⁻/CO₃²⁻
- Booth, 1998 — The Krib: CO₂ table