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Direct Salt Addition Calculator

* Special thanks to Boomer from www.reefcentral.com for his help.

This calculator estimates the weight and volume of salt required to increase salinity to a target level. You should always exercise caution when adding salt directly to an aquarium: add only small amounts at a time and in an area away from invertebrates or fish. If mixing up new saltwater, set "Current Salinity" to 0 ppm.

Tell Me About Water Impurity in Salt Mix

All salt mixes contain some water content. If 35 grams of a given salt mix are collected, typically 4 - 7 of these grams turn out to be water. To estimate the water content of your salt mix, add 35 grams of salt mix to 965 grams of RO/DI water and measure the resulting salinity in parts-per-thousand. Subtract this number from 35 to get your water content.

For your convenience, the water content of several common brands are presented below. These brands were professionally tested by Marlin Atkinson and Craig Bingman back in 1999, so these data may be outdated.

Salt Mix Water Content in 35 Grams of Salt Percentage Water Weight
Coralife 6.61 g 18.9%
HW Marine Mix 5.60 g 16.0%
Instant Ocean 5.35 g 15.3%
Kent 6.15 g 17.6%
Red Sea Salt 4.93 g 14.1%
Reef Crystals 6.09 g 17.4%
SeaChem 5.46 g 15.6%
Tropic Marin 2.36 g 6.7%

Water Volume:

Current Salinity:

Target Salinity:


Water Impurity in Salt Mix:

Salt Weight Required:

Estimated Salt Volume Required:

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For more information please contact me as "TheH" on www.reefcentral.com