The salt content in saltwater is usually measured as specific gravity (also sometimes called relative density) and is one of the most important water parameters. Many tank inhabitants are sensitive to even minor changes of the water conditions. These should therefore be kept as constant as possible in the optimum range for each tank.

The specific gravity of natural seawater of 35 ‰ (psu*) is 1.026 – compared to water measured at 25 °C / 77 °F.

Our recommendation for aquarium water at 25 °C is 1.025 - 1.027 (depending on the tank type), which can be read in the blue part of the scale on the Tropic Marin® High Precision Hydrometer.

Tropic Marin® Measuring Cylinder:

• Height: 36 cm / 14 inches

• Content: 500 ml / 17 fl. oz.

• Made of transparent plastic (PP - polypropylene)

• With stable basis and spout

• Molded graduations

Tropic Marin® High-Precision Hydrometer: 

• Maximum deviation: 0.001 at 25 °C / 77 °F

• Scale from 1.021 à 1.031

• Resolution: 0.0001

• Recommended range: 1.025 to 1.027 (at 25 °C / 77 °F)