Aquarium Salt & Salinity Calculator
What is the Aquarium Salt & Salinity Calculator?
This calculator tells you how much salt mix to add to reach your target salinity. Whether you’re filling a new reef tank or mixing water for a water change, you need the right amount of salt per gallon or liter.
We use standard reef salinity (35 ppt / 1.026 SG) as the reference. You can choose ppt (parts per thousand) or specific gravity. Always mix salt in a bucket until fully dissolved before adding to the tank.
How to Use This Calculator
- Enter your tank volume or dimensions (we’ll estimate volume).
- Set your target salinity in ppt or specific gravity, or pick a preset (Reef, Fish-only, Brackish).
- Read the result: grams (primary), plus kg/lbs and a very approximate cups estimate.
- Mix the salt in a separate container with water until fully dissolved, then add to the tank.
How would you like to enter your tank info?
Tank dimensions
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Enter Your Tank Dimensions
Target salinity
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What is the Aquarium Salt & Salinity Calculator?
This calculator tells you how much salt mix to add to reach your target salinity. Whether you’re filling a new reef tank or mixing water for a water change, you need the right amount of salt per gallon or liter.
We use standard reef salinity (35 ppt / 1.026 SG) as the reference. You can choose ppt (parts per thousand) or specific gravity. Always mix salt in a bucket until fully dissolved before adding to the tank.
How to Use This Calculator
- Enter your tank volume or dimensions (we’ll estimate volume).
- Set your target salinity in ppt or specific gravity, or pick a preset (Reef, Fish-only, Brackish).
- Read the result: grams (primary), plus kg/lbs and a very approximate cups estimate.
- Mix the salt in a separate container with water until fully dissolved, then add to the tank.
Aquarium Salinity: Why It Matters and How to Get It Right
Salinity is the amount of dissolved salt in your water. In the ocean it’s around 35 parts per thousand (ppt), or 1.026 specific gravity. Reef and saltwater tanks aim for the same range so fish and corals experience stable chemistry.
Why Not Add Salt Straight Into the Tank?
Undissolved salt can sit on rocks and sand and burn corals and fish. It also causes local spikes in salinity. Always mix salt in a bucket or barrel with water (and a pump or stirrer if you have one) until it’s fully dissolved and clear, then add that water to the tank.
Matching Water Changes to Tank Salinity
When you do a water change, the new water should match your tank’s salinity. If your tank is 35 ppt, mix your change water to 35 ppt. That way you avoid swings that stress fish and corals. Use this calculator to get the right amount of salt for the volume you’re mixing.
Measuring Salinity Accurately
Refractometers are more accurate than hydrometers and are the standard for reef keepers. Many are most accurate when calibrated with a 35 ppt / 1.026 calibration fluid rather than at 0 ppt. Temperature affects readings—many refractometers are calibrated for 20°C (68°F). Digital salinity pens are convenient but need calibration too. Always use a scale (grams) for the initial mix and a refractometer for the final check—never rely on cups for the final dose.
Real-World Variables
Displacement: rocks and sand take up space. A 45‑gallon tank with 80 lbs of rock might hold only ~35 gallons of actual water; dosing for 45 gal would overshoot salinity. For water changes, mix in a bucket and use the bucket volume—that’s accurate. Salt brand: some fortified or “pro” mixes require slightly more or less weight per liter for the same specific gravity. Moisture: if the salt bag was left open and absorbed humidity, the salt is heavier per scoop but has less actual sodium chloride per 100 g. When in doubt, aim slightly under the calculated amount and add more mix after measuring—easier than diluting to lower salinity.