One used Tropic Marin High precision Hydrometer for determining the specific gravity in aquariums.

Many tank inhabitants are sensitive even to minor changes of the water conditions. For an exact, reliable measure of the specific gravity, Tropic Marin® offers a high-precision instrument. The hydrometer is handmade and designed to float vertically in the water. The maximum deviation is about 0.001 at 77° F (25° C).

Length of the hydrometer: 14″.