THE REEF SEA METER

NATURAL SEA WATER REFRACTOMETER

Specifically designed for aquarium use for measuring the salinity of Natural Sea Water (NSW)

Specifications:

Almost all hand held salt water refractometers available to the hobby are designed and calibrated for the testing of brine solutions, i.e. sodium chloride, and are not calibrated for the refractive index of Natural Sea Water.  This is a very important distinction.  Other Salinity Refractometers used for marine aquariums are designed to test salt in water – nothing else!  The Reef Sea Meter is designed to measure Salinity of Natural Sea Water taking into account the other elements that comprise salinity in the marine water sampled.

Even though the largest percentage of salt in the sea is sodium chloride, the presence of other significant ions such as magnesium and calcium in natural sea water results in a different refractive index relative to that of brine. A standard salt (brine) refractometer will therefore not give the correct salinity for Natural Sea Water and a conversion factor must be applied.

MEASURING THE SALINITY OF YOUR AQUARIUM

Ensure that the prism of your Refractometer is clean by washing the prism plate and cover plate after use each time in pure water and drying it with the polishing cloth supplied.  Why?  The prevent corrosion of the unit and to ensure that your readings are accurate. 

Take a representative sample of the water from your aquarium or other marine habitat.

Allow the water to acclimate to the temperature of the instrument for 15 seconds and then look down the eyepiece to take the salinity reading at the bottom of the blue and clear interface.

SALINITY AND SPECIFIC GRAVITY STANDARDS

We recommend that you try to get used to thinking in terms of salinity and use the salinity readings on the Refractometer as this is the scale that is calibrated against the refractive index standard.

SALINITY is always constant whereas Specific Gravity, although more commonly used in the hobby, is fraught with misconceptions that are explained later.

Salinity as explained earlier in these instructions is generally described as the mass of salt in a specific mass of pure water and is normally expressed in parts per thousand or ppt (‰).

For example 35ppt could be 35 grams of salt in 965 grams of pure water or 35 tons of salt in 965 tons of pure water - 35 units by weight in a total of 1000 units by weight. Weight is never affected by temperature.

In the oceans the salinity varies from 5 ppt in the Northern Baltic Sea to 40 ppt in the Northern Red Sea with a generally accepted global average of 35ppt for NSW. The level that you keep your aquarium at will generally be determined by the type of animals that you keep in the system.

Often fish only systems are maintained at lower salinities down to 29ppt as it exerts less osmotic stress on the fish whereas reef systems are normally maintained at 35-36ppt.

SPECIFIC GRAVITY is not an exact scale and is defined as the relationship between the density of a solution, in this case seawater, relative to the density of pure water – normally measured directly by hydrometer.

As density is temperature dependent due to expansion, which changes the volume for a given mass, then specific gravity is also temperature dependent and varies according to two parameters.

1 - The temperature of the test sample during measurement – normally the tank temperature at 25’C/77’F

2 – The temperature at which the pure water (distilled or R/O) density used in the SG calculation was measured at – normally the calibration temperature that should be printed on all good scientific hydrometers.

This leads to huge misunderstandings within the hobby as to what the specific gravity should be specified at within the aquarium. Most people believe that the SG of 35ppt seawater is 1.025 at 25’C/77’F whereas in reality the specific gravity measured is determined by the calibration temperature of the particular hydrometer owned by the user.

The specific gravity readings in the table above range from 1.0233 – 1.0277 however they are all correct in describing the same sample of water at 35ppt salinity.

The difference between the readings is due solely to the calibration temperature which is used to set the scale for the instrument.

From this we can see how non specific S.G. is as a way of describing the salinity of the water in your aquarium.

The Reef Sea Meter  Refractometers are calibrated at 20’C/68’F and so the calculated specific gravity at 35ppt displays a reading of 1.0266. This is the equivalent to a specific gravity reading of 1.0264 for a water sample temperature of 25’C/77’F using a standard hydrometer that has a calibration temperature of 25’C/77’F

IMPORTANT!  HIGH QUALITY! 

EACH UNIT COMES WITH A 3 YEAR WARRANTY AGAINST DEFECTS.  FREE REPLACEMENT PARTS IF YOU EVER NEED THEM!

  OURS ARE MADE OF STURDY ALUMINUM!  

GOT A REEF SHOP OR REEF CLUB?  BUY FROM US!

YOU CAN CALL, FAX OR E-MAIL US IF YOU EVER HAVE ANY QUESTIONS.  

Included are: A plastic, foam-lined hard case, a pipette for dropping test fluids onto the prism (never dip the refractometer into the test fluid!), a mini screwdriver for scale calibration, and a Users Guide.

Questions? Larger Orders? Please feel free to call, fax or e-mail!

National Industrial Supply
30777 Rancho California #891420
Temecula, CA 92589, USA
Sales: 951.308.9269
Fax: 310.833.7306 

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