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Water chemistry

Stable water, without the guesswork

Read your water clearly: hardness, CO₂, mixing, and salinity become useful numbers you can act on.

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GH hardness conversion

Convert general hardness between German degrees, French degrees, ppm, and mmol/L.

GH (°dH)8
TH (°fH)14.29
ppm CaCO₃142.8
mmol/L1.4264

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.

KH (°dKH)4
TAC (°fH)7.14
ppm CaCO₃71.4
meq/L1.4264

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.

CO₂ (mg/L)19
ResultOptimal for plants (15–30 mg/L)

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.

Source 1 (e.g. tap water)40%
Source 2 (e.g. RO water)60%
Source 1 liters40
Source 2 liters60

Formula

C₁V₁ + C₂V₂ = Cₜ(V₁ + V₂)

Density & salinity (marine)

Convert between density, specific gravity, salinity (ppt), and conductivity for marine aquariums.

Density (g/cm³)1.028
Specific gravity (SG)1.028
Conductivity (mS/cm)52.5
Salt to add360g

The gram correction assumes roughly 1 g/L per 1 ppt: always dissolve salt separately and verify with a calibrated refractometer.

Scientific references