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Old 04-09-2005, 01:06 PM   #28
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Originally Posted by nim75sg
Wei Leong ... That was my initial impression of this digital lab grade tester being not as accurate as the refractometer.

But I was wrong, it was as accurate or rather on par with the refractometer getting the same readings other than it ease of use over the refractometer which is a plus for me.

For the benefit of reefers, here is the background operation behind a "digital" and "analog" salinity tester adopted with the courtesy of JBJlighting.Com

How does the Digi-Lab Grade Tester compare to a refractometer?

1. The Digi-Lab TSS is in the family of conductivity meters, which are recognized as the most accurate, precise, and reliable measurement methods used in the scientific industry. Ease of use, automatic conversions, and multi-parameter testing in a single tester are the primary benefits.

a. How it Works: Salt exists as sodium and chlorine ions that are positively and negatively charged moving freely in water. Once an electrical field is present, positively charged ions move toward a negatively charged electrode, and negatively charge ions move towards a positively charged electrode to obtain a reading.

b. Application: Simply dip the probe into the aquarium and press a button to receive an instant display of temperature (F), salinity (ppt), and temperature compensated specific gravity (eg.1.024)

2. Refractometer Measures the salt level by a Refractive Index.
a. How it Works: A refractometer works on the principle that the speed of light varies depending on the density of the medium that it travels through. Hence, the less dense the medium, the faster light travels. When light passes from a medium of one density to a medium of another density at an angle, the rays of light are refracted and displayed onto a scale on the refractometer.

b. Application: Add a few drops of water onto a prism located on top of the refractometer. Water must cover the entire prism and must be free of air bubbles to obtain accurate results. Turn dial until scale is focused to obtain a reading in the direction of a light source.
But then sea water consists of alot more than sodium and chloride ions. Very significant amount of Mg/Ca also exists.
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