H2Ocean True Seawater Refractometer

H2Ocean True Seawater Refractometer

The H2Ocean True Seawater Refractometer is a handheld salinity tester that measures the true salinity and specific gravity (S.G.) of natural seawater by refractive index. It suits marine and reef aquarists who want a seawater refractometer with a scale calibrated for the real thing, rather than a brine-based scale that needs a conversion factor.

Why a True Seawater Refractometer?

Almost all other handheld saltwater refractometers sold to the hobby are designed and calibrated for brine solutions (sodium chloride) and are not calibrated for the refractive index of natural seawater. Sodium chloride is the largest percentage of the salt in the sea, but significant ions such as magnesium and calcium give natural seawater (NSW) a different refractive index from brine. A standard brine refractometer therefore won't give the correct salinity for natural seawater unless a conversion factor is applied. This D-D refractometer is calibrated for seawater. When correctly calibrated, it gives true salinity results for aquarium use, with greater accuracy than was previously attainable.

Key Benefits

• Made for seawater: the scale is calibrated for the refractive index of natural seawater, not brine
• Gives true salinity and specific gravity readings without a conversion factor
• Accurate automatic temperature compensation (ATC)
• Easy-to-read display with a scale of 0-40ppt
• Copper body that responds faster to ambient temperature changes than other materials
• Handheld, so you can test straight from the aquarium or sump

Easier to Read

Most refractometer scales read from 0-100ppt, yet reef keepers only really care about the 30-40ppt region. This refractometer reads from 0-40ppt, which gives 2.5 times the resolution of a normal 0-100 scale.

How Auto Temperature Compensation Works

Salinity is the mass of salt in a mass of water, so it does not change with temperature. A refractometer doesn't measure salinity directly. It measures the refractive index and displays it as salinity, and the refractive index of a solution does vary with temperature. This means a refractometer reading is always temperature dependent.

• An ATC refractometer has a bimetal strip inside that moves the reading scale as the temperature changes, compensating for the change in refractive index.
• It is the temperature of the instrument, not the water temperature, that matters. The small test sample equilibrates to the temperature of the refractometer within seconds.
• Once correctly calibrated at the set calibration temperature of 20°C, the refractometer can be used wherever the ambient (and therefore instrument) temperature warms or cools within the ATC range of 10 to 30°C.

How to Use

• Calibrate with the instrument at 20°C, which is close to the average room temperature in most cases.
• Let the refractometer stand at this temperature for 30 minutes to equilibrate before calibrating.
• Use a light source as close to daylight as possible. Refractive index also depends on the wavelength of light.
• Test with a small water sample. It will equilibrate to the instrument's temperature within seconds.

Calibration Reference

D-D refractometers are calibrated at 20°C. At 35ppt, the calculated specific gravity displays a reading of 1.0266. This is equivalent to a specific gravity reading of 1.0264 for a water sample at 25°C, using a standard hydrometer with a calibration temperature of 77°F or 25°C.

Suitable For

• Marine and reef aquariums filled with natural or mixed seawater
• Hobbyists who want true salinity and specific gravity readings, rather than a brine-scale reading corrected with a conversion factor

Specifications

• Type: handheld seawater refractometer with automatic temperature compensation (ATC)
• Scale: 0-40ppt, 2.5 times the resolution of a 0-100ppt scale
• Calibration temperature: 20°C
• ATC range: 10 to 30°C
• Body material: copper
• Reading at 35ppt (calibrated at 20°C): specific gravity 1.0266

What's Included

• One H2Ocean True Seawater Refractometer

Frequently Asked Questions

How is a true seawater refractometer different from a standard salt refractometer?
A standard refractometer is calibrated for brine (sodium chloride). Natural seawater also contains ions such as magnesium and calcium, which change its refractive index, so a brine unit needs a conversion factor. This model's scale is calibrated for natural seawater.

What temperature should I calibrate it at?
Calibrate at 20°C, and let the instrument stand at that temperature for 30 minutes first so it can equilibrate.

Does the water temperature affect my reading?
It is the instrument's temperature that matters. The small water sample reaches the refractometer's temperature within seconds. Once calibrated at 20°C, the ATC covers instrument temperatures from 10 to 30°C.

Why does the scale only go up to 40ppt?
Aquarium salinity sits in the 30-40ppt region, so the 0-40ppt scale gives 2.5 times the resolution of a normal 0-100ppt scale, which makes it easier to read.

What specific gravity should it show at 35ppt?
Calibrated at 20°C, it shows 1.0266 at 35ppt. That equals 1.0264 for a sample at 25°C on a standard hydrometer calibrated at 77°F (25°C).

What kind of light should I use when reading it?
Use a light source as close to daylight as possible, because refractive index also depends on the wavelength of light.

When can I expect delivery?

• Gauteng (Jhb/Pta) - 1-3 working days
• Nationwide (Cpt/Dbn+) - 2-5 working days
• Outlying Areas - 3-7 working days

All orders are sent via Economy Road, typically through Fastway or Internet Express Couriers*. Estimated timeframes are not guaranteed. Once the order is collected by the courier, we have no control over third-party logistics and cannot make any time promises.

If you prefer a faster 🚀 shipping option, we also offer The Courier Guy during checkout in the dropdown selection. Please note that this option is not free, and you must choose it to use it. Please pay careful attention to the cutoff times and delivery timeframe for these options during checkout.

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Delivery times to lockers and pickup locations typically range from 2–7 working days, depending on your location.*

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Collection timeframes:

• Bob Box: Collect within 2 days of receiving your collection notification.
• PUDO Lockers: Collect within 36 hours of receiving your collection PIN or SMS notification.

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