All salt mixes contain some water content. If 35 grams of a given salt mix are collected, typically
2 - 7 of these grams turn out to be water weight. The actual number varies by brand and production
lot, but most salt mixes range between 4 - 7 grams of water in every 35 grams of salt mix.
To estimate the water content of your salt mix, add 35 grams of salt mix to 965 grams of RO/DI water
(at 25C/77F this is ~968 ml of water; at 20C/68F this is ~967 ml of water), and measure the resulting
salinity in parts-per-thousand. Subtract this number from 35 to get your water content. For example,
if you measure 32 then your water content would be 35-32, or 3 grams of water in every 35 grams of
salt mix.
For your convenience, the water content of several common brands are presented below. Note that 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by Marlin Atkinson and Craig Bingman back in 1999, so these data may be outdated.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% |
|