D&D Refractometer

The refractometer Deltec measure the density and salinity with reliability and precision.

Refractometer DD 

Portable instrument for measuring the TRUE salinity and specific gravity (SG) of seawater by refractive index.

In what way does the refractometer... DD Is seawater different?

Almost all portable saltwater refractometers available for hobbyists are designed and calibrated to test brine solutions, that is, sodium chloride, and are not calibrated for the refractive index of natural seawater.

Even though the largest percentage of salt in the sea is sodium chloride, the presence of other important ions such as magnesium and calcium in natural seawater results in a different refractive index compared to brine. Therefore, a standard salt (brine) refractometer will not provide the correct salinity for natural seawater (NSW), and a conversion factor must be applied.

For example, a 35 ppm NSW solution has the same refractive index as a 36.5 ppm brine solution.

After extensive development, the new D-D ATC refractometer addresses this issue as the scale is calibrated for seawater, providing accurate salinity readings for aquarium use when properly calibrated and with greater precision than previously possible.

Our refractometers are equipped with an internal copper body that conducts heat more quickly than the cheaper aluminum and plastic versions, allowing for faster and more accurate automatic temperature compensation.

One of the other issues with most refractometers is that the displayed scale typically reads from 0 to 100ppt, while we are really only interested in the 30 to 40ppt range. Our new seawater refractometer has therefore been specially designed to read from 0 to 40ppt, giving you 2.5 times the resolution of a normal 0 to 100 scale.

Automatic Temperature Compensation (ATC)

There are many misunderstandings regarding the functioning of the ATC feature and its effect on the refractometer at different ambient room temperatures.

Salinity is a measure of the amount of salt in a mass of water and therefore does not vary with temperature.rature.Toutefois, A refractometer does not directly measure salinity but measures the refractive index, which is then displayed as salinity. The refractive index of a solution varies with temperature; therefore, the reading you obtain with a refractometer always depends on the temperature.

An ATC refractometer has a bimetallic strip inside the instrument that shifts the reading scale when the temperature changes to compensate for the change in the refractive index. What people generally don't understand is that it is the temperature of the instrument, not the water temperature, that is important because the small water sample used for testing will equilibrate to the temperature of the refractometer within a few seconds.

Once properly calibrated at the set calibration temperature of 20°C, the refractometer can then be used in environments where the ambient temperature, and thus the temperature of the instrument, would warm up or cool down within the ATC range, which is between 10 and 30 degrees Celsius.

Calibration

If you look at the scale above, you will see that the refractometer indicates that it is calibrated to and displays the SG of seawater at 20°C.

Most salt refractometers use this temperature and will be marked 20C or 20/20. Calibration should always be performed with the instrument at 20°C, which is close to the average ambient temperature in most cases. Allow the refractometer to rest at this temperature for 30 minutes to equilibrate.

The refractometer DD It is designed with a copper body, which is more expensive to manufacture but responds more quickly to changes in ambient temperature compared to other materials.

Note that the refractive index also depends on the wavelength of the light and, therefore, a light source that is closest to daylight should also be used.

Refractometers DD They are calibrated at 20°C, and thus the density calculated at 35ppt displays a reading of 1.0266. This is equivalent to a specific gravity reading of 1.0264 for a water sample temperature of 25°C using a standard hydrometer that has a calibration temperature of 77°F or 25°C.

Instructions

INSTRUCTIONS FOR THE NATURAL SEAWATER REFRACTOMETER ATC

Portable instrument for measuring salinity and specific gravity (SG) by refractive index.

Specifically designed for use in aquariums to measure the salinity of natural seawater.

Almost all portable saltwater refractometers available for recreational use are designed and calibrated for testing solutions of...brine, that is to say, sodium chloride, and are not calibrated for the refractive index ofnatural seawater.

Even though the largest percentage of salt in the sea is sodium chloride, the presence of other important ions such as magnesium and calcium in natural seawater results in a different refractive index compared to brine.

A standard salt (brine) refractometer will not provide the correct salinity fornatural seawater(NSW) and a conversion factor must be applied.

For example, a solution of 35 ppm NSW has the same refractive index as a solution of 36.5 ppm brine. When using a standard brine refractometer, the user should therefore look for a reading of 36.5 ppt when trying to obtain a reading of 35 ppt.natural seawater.

EASIER TO READ

One of the other problems with most refractometers is that the displayed scale usually reads between 0-100ppt when we are really only interested in the 30 to 40ppt range.

Our new seawater refractometer has been specially designed to read from 0 to 40ppt, giving you 2.5 times the resolution of a normal 0-100 scale.

AUTOMATIC TEMPERATURE COMPENSATION (ATC)

There are many misunderstandings regarding the functioning of the ATC feature and its effect on the refractometer at different ambient room temperatures.

Salinity is a measure of the mass of salt in a mass of water and therefore does not vary with temperature; however, a refractometer does not measure salinity directly but measures the refractive index, which is then displayed as salinity. The refractive index of a solution varies with temperature; consequently, the reading you obtain with a refractometer is always dependent on the temperature.

An ATC refractometer has a bimetallic strip inside the instrument that shifts the reading scale when the temperature changes to compensate for the change in the refractive index.

What people generally do not understand is that it is the temperature of the instrument and not the temperature of the water that is important because the small water sample used for the tests will equilibrate to the temperature of the refractometer in a few seconds.

Once correctly calibrated at the set calibration temperature of 20°C, the refractometer can then be used in environments where the ambient temperature, and thus the temperature of the instrument, would heat up or cool down within the ATC range, which is between 10 and 30 degrees Celsius.

CALIBRATION

If you look at the scale above, you will see that the refractometer indicates that it is calibrated and displays the SG of seawater at 20°C. Most salt refractometers use this temperature and will be marked 20°C or 20/20.

Calibration should always be performed with the instrument at 20°C, which is close to the average room temperature in most cases. Allow the refractometer to rest at this temperature for 30 minutes to equilibrate.

The refractometer DD is designed with a copper body, which is more expensive to manufacture but responds more quickly to changes in ambient temperature than other materials.

Step 1: Clean the glass prism and the cover flap of the refractometer with pure water or reverse osmosis water to ensure there are no salt residues that could affect the reading.

Step 2: Using the provided dropper, fill and empty the dropper several times with pure or RO water, and then, while holding the refractometer horizontally, place a water sample on the glass prism.

Step 3: Close the transparent cover over the sample and wait 15 seconds for the temperature to equilibrate with the instrument before looking through the eyepiece with the prism end directed towards a bright light source. The eyepiece can be screwed in or out to adjust the focus and compensate for individual vision.

Note that the refractive index also depends on the wavelength of light, and therefore a light source closest to daylight should also be used..

You will notice that the top of the viewing screen is blue, and where it transitions from blue to clear at the bottom is where the reading should be taken. If this boundary does not exactly align with the zero mark on the scale, then take the small screwdriver provided and, after removing the protective cap, adjust the position of the scale by tightening or loosening the screw.

Your refractometer is now calibrated.

Note that it is also possible to calibrate the refractometer using a 35ppt reference solution, but be wary of any versions that do not mention the calibration temperature, as they may be designed to be used or calibrated at a different temperature.

MEASURING THE SALINITY OF YOUR AQUARIUM

Make sure that the prism of your refractometer is clean by washing the prism plate and cover after each use. Dip it in pure water and dry it with the provided polishing cloth.

Take a representative sample of the water from your aquarium, making sure to fill and empty the dropper several times to first rinse away any salt deposits from a previous use. Then, place the water sample on the prism in the same manner as during the calibration process. It is better to put more water on the plate and let the cover plate push the excess away rather than using too small a volume.

Allow the water to equilibrate to the instrument's temperature for 15 seconds, then look through the eyepiece to take the salinity reading at the bottom of the blue and clear interface. One side of the scale will let you read the salinity and the other the specific gravity calculated at 20°C for pure water density **.

STANDARDS OF SALINITY AND SPECIFIC GRAVITY

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

SALINITY...is always constant whereas specific gravity, although more commonly used in recreational contexts, is fraught with misconceptions that will be explained later. Salinity, as previously explained 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 for a total of 1000 units by weight. Weight is never affected by temperature. In the oceans, salinity varies from 5 ppt in the northern Baltic Sea to 40 ppt in the northern Red Sea, with a globally accepted average of 35 ppt for NSW. The level at which you maintain your aquarium will generally be determined by the type of animals you keep in the system.

Often, fish-only systems are maintained at lower salinities, up to 29ppt, because they exert less osmotic stress on the fish, whereas reef systems are normally maintained at 35-36ppt.

The printed parameters for H2Ocean Pro+ reef salt are indicated at a salinity of 35.5 ppt.

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 a hydrometer.

Since density depends on temperature due to expansion, which changes the volume for a given mass, density also depends on temperature and varies based on two parameters.

1 - The temperature of the sample to be tested during the measurement - normally the reservoir temperature at 25°C

2 - The temperature at which the density of pure water used in the calculation of SG was measured at – normally the calibration temperature that should be printed on all good scientific hydrometers. This leads to enormous misunderstandings in the hobby regarding what specific gravity should be specified in the aquarium. Most people believe that the SG of 35ppt seawater is 1.025 at 25 °C when in reality the specific gravity measured is determined by the calibration temperature of the particular hydrometer belonging to the aquarist.

The specific gravity readings in the table for

The left range from 1.0233 to 1.0277

However, they are all correct in describing the same water sample with 35 ppt salinity. The difference between the readings is solely due to the calibration temperature used to set the instrument's scale.

From there, we can see how SG is not specific for describing the salinity of your aquarium water.

Refractometers DD are calibrated at 20 °C, and thus the density calculated at 35 ppt displays a reading of 1.0266.This corresponds to a specific gravity reading of 1.0264 for a water sample at a temperature of 25°C using a standard hydrometer that has a calibration temperature of 77°F or 25°C.