Specific gravity measures the relative salinity (number of dissolved salts) in your aquarium water in comparison to pure water. Measuring specific gravity on a regular basis is crucial to maintaining the ideal environment for your marine inhabitants. The following helpful tips will ensure accurate results when measuring specific gravity.

• Most hobbyists use a simple hydrometer or a refractometer to measure salinity.
• For professional results consider a portable refractometer or a high-tech electronic salinity monitor.
• Before changing your aquarium water, measure and record the specific gravity. Make sure the new saltwater matches the specific gravity of your aquarium. Too much of a deviation in salt levels could shock or potentially kill sensitive aquarium inhabitants.
• Replenish evaporated water with clean freshwater - not prepared salt water. Remember, salts remain behind after water evaporates. If you top off your aquarium with salt water, you are compounding salt levels in your aquarium.
• Before using a new swing-arm hydrometer, condition or season the hydrometer by soaking it in saltwater for 24 hours.

Reef Aquarium: 1.023 to 1.025
FOWLR Aquarium: 1.020 to 1.02

What is a refractometer?

Serious hobbyists know that the best way to measure the salinity and specific gravity of aquarium water is to use a refractometer. These precision optical instruments are incredibly accurate even at very low salt levels and are equally easy to use. Recently, these instruments have become more affordable, so now every aquarium owner can have one to help monitor water conditions.

How do you use a Refractometer?

Place 1 to 2 drops of aquarium water onto the prism glass and close the plate cover. Once a fluid sample is placed on the measuring surface, the light passing through it slows and bends. The refractometer focuses this bent light on a tiny internal scale. The scale is magnified by the eyepiece lenses, so it is easily visible.

Look through the eyepiece and view the scale. The top portion of the scale appears blue, and the bottom part appears white. Take your reading at the intersection of these two colors. One side of the scale measures salinity and the other side measures specific gravity.

To effectively monitor your marine aquarium water conditions, consider investing in a refractometer. The accuracy and affordability make it worthwhile.

Salinity & Specific Gravity are easily viewed when looking through the Refractometer

Accurately test your aquarium's salinity with a Portable Refractometer. The portable Refractometer is an optical instrument that gives a direct, temperature compensated reading of specific gravity and salinity, and is overall simple to use.

Swing-arm styled Instant Ocean Hydrometer economically tests your aquarium's salinity and specific gravity.