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Measuring Cylinder & Hydrometer

For determining the specific gravity with a hydrometer in saltwater aquaria



Product description

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.


Product features

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)



The Tropic Marin® Measuring Cylinder is made of PP (polypropylene). The Tropic Marin® High-Presision Hydrometer is made of mouth-blown glass. Made in EU.



NOTE: The specific gravity is temperature dependent. With increasing temperature the specific gravity decreases. Therefore, the measured water temperature should be 25 °C / 77 °F to obtain a correct result.For an exact, reliable measure of the specific gravity, we recommend to use the Tropic Marin® High Precision Hydrometer.

  • Fill the measuring cylinder with maximum 400 ml saltwater (water temperature = 25 ° C / 77 °F).

  • The hydrometer should be dry and clean.

  • Gently place the hydrometer into the water until it floats freely.

  • Now read the specific gravity on the blue part of the scale of the hydrometer at the level of the water surface - NOT at the level of the meniscus, which is creeping higher at the edges!

  • To avoid any distortion of future measurements, rinse the measuring cylinder well with fresh tap or reverse osmosis water to remove salt residues after each use.


DO NOT CONFUSE: The “Tropic Marin® Aräometer”, which is used in German speaking countries, has a scale with a green printing and the indication ‘Dichte/density’.


We recommend different salinities for various tank types:




Other product recommendations

Tropic Marin® Sea Salt Classic is an ideal foundation for the care and growth of all marine organisms in an aquarium and to maintain the alkalinity in a 9-10 °dH range. Especially for reef aquaria we recommend the use of Tropic Marin® Pro-Reef Sea Salt. This salt has an optimized concentration of calcium and magnesium, which promote the growth of corals and maintain the alkalinity in a 7-8 °dH range.

For the daily supply of calcium and carbonate hardness, we recommend the new Tropic Marin® Carbo-Calcium or the application of the well-known Balling method with Tropic Marin® Original Balling Components.

Frequently asked questions

Answers to frequently asked questions about this product can be found in our FAQ section.

Container sizes

Measuring Cylinder                                                    Art. Nr. 51000                             

Hydrometer Determining the specific gravity         Art. Nr. 51002

Measuring Cylinder  incl. Hydrometer                     Art. Nr. 51022              


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