Salt Mix / Salinity Calculator

Why mix rate is an input, not a fixed constant

Different reef salt brands are formulated to reach a target salinity at slightly different dry-weight ratios, and some are designed around a somewhat different target specific gravity out of the bag. Rather than assuming one brand's number, this calculator lets you enter your specific product's recommended grams-per-liter rate (usually printed on the bag or in the product's mixing instructions) and does the volume math for it. A default of 35 g/L is provided as a reasonable placeholder near natural seawater salinity if you don't have your product's exact figure handy.

Why the cup conversion is only approximate

Dry salt mix bulk density (how much a given volume weighs) varies by brand and even by batch, since it depends on grain size and moisture content. The gram and ounce figures are exact for your entered rate; the cup conversion is a rough convenience estimate and shouldn't be relied on for precise mixing — weigh your salt mix on a scale when precision matters.

Mixing and testing

Mix salt into RO/DI or otherwise purified water with a powerhead or pump running, let it fully dissolve and circulate (often several hours, sometimes overnight for full clarity), then test actual salinity with a refractometer or quality hydrometer before using the water — treat the calculated amount as a starting point to mix toward your target, not a guarantee of the exact final reading.

Source: Mix-rate math follows the gram-per-liter dosing convention published on major reef salt mix product labels (e.g. Instant Ocean, Red Sea); always check your specific product's own ratio.