How to use this aquarium salt mix calculator
Read the complete product instructions and select their volume basis. Enter the volume and dry product mass stated in the reference recipe for your independently chosen salinity and conditions. Use the same volume basis for the batch you want to prepare. Select liters, US liquid gallons, or imperial gallons and grams, kilograms, ounces by mass, or pounds. The recipe mass starts blank because the calculator cannot know your product. Changing volume basis clears it and requires a fresh recipe check.
How the calculation works
Recipe scaling keeps one documented proportion intact. Divide desired batch volume by reference recipe volume to obtain a scale factor, then multiply reference dry product mass by that factor. A recipe of 380 g for 10 L and a desired batch of 25 L has a scale factor of 2.5, giving 950 g. Those are illustrative quantities for explaining arithmetic, not a generic recipe for all marine salts or an assurance that a particular salinity will result.
The volume basis is essential. Some instructions describe how much dry product to add per starting quantity of freshwater; others define a final quantity of mixed saltwater. Dissolving a product can change the finished solution volume. A starting-water recipe must therefore be scaled using starting-water volume, and a finished-mixture recipe using finished volume. Selecting one basis does not convert it into the other. This calculator has no density or volume-expansion model with which to perform that conversion.
Manufacturer documentation demonstrates why a universal dry dose would be misleading. Tropic Marin gives product-specific mixing instructions, while Red Sea's laboratory-preparation notes explicitly distinguish starting water from making up a final mixed-water volume. These are evidence for retaining the recipe's method, not permission to combine two brands' instructions or apply an analytical preparation procedure to every household batch. Always follow the full instructions for the product actually being weighed.
A salinity reading is not simply the mass of an arbitrary commercial dry mix per liter of starting water. Reporting conventions, solution density, product composition, and water associated with the ingredients can affect the relationship. In particular, a 35 ppt label does not establish a universal 35 g/L product recipe. The tool deliberately has no target-ppt or specific-gravity input because it does not implement a validated product-specific salinity model or a temperature-dependent density conversion.
Scaling a recipe also assumes its conditions remain appropriate. Use the same product, compatible source water, and the instructions' preparation method. Check the actual prepared batch with suitably calibrated equipment rather than relying on calculated mass alone. The tool does not choose a salinity for fish or corals, measure the water, account for a scale's error, or verify that a stored salt product has the same properties as the reference. Numeric precision cannot remove those missing observations.
Formulas
Recipe scale factor
Dry product mass
Mass display conversion
Worked examples
Scale a starting-freshwater recipe
Suppose your verified product recipe requires 380 g per 10 L of starting freshwater at its stated conditions. For 25 L of starting water, use a scale factor of 25/10 = 2.5. The scaled quantity is 950 g, or 0.95 kg and approximately 33.510 oz by mass. These example values are not a recommended dose; substitute the instructions for your actual product.
Scale a finished-volume recipe without changing its meaning
A separate hypothetical recipe specifies 760 g while making up 20 L of finished saltwater. For 5 L of finished mixture, its scale factor is 5/20 = 0.25, giving 190 g. This does not mean adding 190 g to exactly 5 L of starting water. The final-volume method, verification, and any adjustment must follow the actual product instructions.
Common uses
Resize a preparation batch
Scale a trusted small recipe to the amount you intend to prepare without changing its volume basis. Keep the original product name, conditions, reference mass, and reference volume in a separate record. The calculator itself does not save a verified recipe library.
Compare container and scale units
Convert an existing batch quantity between liters and explicitly identified gallon conventions, or a dry mass between metric and avoirdupois units. Ounces here describe weight, not fluid volume. Unit normalization preserves a quantity; it cannot validate an ambiguous or incomplete recipe.
Accuracy and limitations
The model is direct proportional scaling only. It assumes the same recipe conditions and does not infer mixing yield, exact salinity, specific gravity, chemical composition, or density. Every entered recipe quantity must be finite and positive. Missing mass is shown as a placeholder, never a fabricated numeric dose.
Prepare and verify water separately using the complete marine product's instructions. Table salt, freshwater-treatment salt, and other additives are not interchangeable with a complete marine mix. Do not apply this batch quantity directly to an occupied tank or interpret it as a species-specific salinity recommendation.
Sources and methodology
References support unit conversions, relevant material or energy calculations, and husbandry context where listed. NumUtility's geometric and arithmetic models are explained above; they do not establish safe stocking, maintenance requirements, or structural capacity.
Frequently asked questions
Why is there no default dry salt dose?
The product, reference salinity, preparation method, and volume basis matter. A blank mass field avoids passing off an assumed generic recipe as verified product information. Enter the documented recipe you intend to scale.
Can I calculate how much salt to add directly to my aquarium?
No. This tool scales a separate preparation batch only. It does not assess occupied-tank salinity correction, a safe change rate, freshwater treatment, or direct dry dosing.
Can I enter 1.026 or 35 as the recipe mass?
Not when those numbers are specific gravity or salinity. The mass field requires actual grams, kilograms, ounces by mass, or pounds of the exact dry product for the reference volume.
Should evaporation top-off use this recipe?
This tool does not choose top-off water composition or an additive dose. Evaporation replacement and preparation for a water change are different operations. Use the appropriate husbandry and product instructions instead of treating a batch calculation as top-off guidance.