Tropic Marin High-Precision Hydrometer

Accurate specific gravity readings for saltwater tanks. Specific gravity is one of the most important water parameters in a reef or marine aquarium, and many animals are sensitive to even small changes, so it should be kept as constant as possible. For an exact, reliable measure, Tropic Marin recommends its High-Precision Hydrometer, a glass float hydrometer with a fine scale from 1.021 to 1.031. Want the matching cylinder too? Get the Tropic Marin Hydrometer with Measuring Cylinder kit. Browse more water testing.

How to Measure

1. Fill a measuring cylinder with no more than 400 mL of saltwater at 25 °C / 77 °F.
2. Make sure the hydrometer is dry and clean, then gently place it in the water until it floats freely.
3. Read the specific gravity on the blue part of the scale at the level of the water surface, not at the meniscus, which creeps higher at the edges.
4. Rinse the cylinder well with fresh tap or RO water after each use to remove salt residue that could throw off future readings.

Temperature matters. Specific gravity drops as temperature rises, so the water should be at 25 °C / 77 °F for a correct result.

Specifications

FAQ

What specific gravity should my reef be?
Natural seawater at 35 ppt is 1.026 at 25 °C / 77 °F. Tropic Marin recommends 1.025 to 1.027 for aquarium water, depending on the type of tank.

Does it come with a measuring cylinder?
No, this is the hydrometer on its own. The kit version includes Tropic Marin's 14 in measuring cylinder.

Why does the water temperature matter?
Specific gravity decreases as temperature increases. Measure at 25 °C / 77 °F so the reading matches the scale.

Where do I read the scale?
At the flat water surface, not at the meniscus where the water curves up the glass.