Marine salinity and salt mix calculator
Marine salinity is quoted three ways. Specific gravity depends on temperature; parts per thousand does not, which is why refractometers win.
ppt
ppt
g per litre for 35 ppt
Salt to add
1.000kg
- In grams
- 1000
- Salt for a full fresh mix
- 7.00
- Specific gravity at that temperature
- 1.026 25
- Approximate conductivity
- 54.60 mS/cm
- Density
- 1026.3 kg/m3
- Fresh water to lower salinity instead
- 0.00
- Compared with natural seawater
- 100.0 %
Show the working
- Water volume = 200
- Target salinity = 35
- Current salinity = 30
- Salt mix strength = 35
- Temperature = 25
- increase = max(35 - 30, 0) = 5
- In grams = 200 * 5 / 35 * 35 = 1000
- Salt to add = 1000 / 1000 = 1
- Salt for a full fresh mix = 200 * 35 / 1000 = 7
- Specific gravity at that temperature = 1 + 35 * 0.00075 - (25 - 25) * 0.00025 = 1.026 25
- Approximate conductivity = 35 * 1.56 = 54.6
- Density = 1000 * 1.026 25 = 1026.25
- Fresh water to lower salinity instead = 35 > 0 && 30 > 35 ? 200 * (30/35 - 1) : 0 = 0
- Compared with natural seawater = 35 / 35 * 100 = 100
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- salt needed = volume x salinity increase / 35 x salt per litre for 35 ppt
- specific gravity rises about 0.00075 per ppt and falls with temperature
Natural seawater is about 35 ppt, specific gravity 1.0264 at 25 degrees. Reef tanks are usually kept at that figure.
Never add dry salt to a tank with livestock in it. Mix it in a separate container and let it dissolve fully.