Bluelab ppm Pen - Manual (Page 7)

8.0 Information about the scales available on the
Bluelab ppm Pen
EC
Is a measure of electrically charged nutrient ions in a solution and is the only
absolute measure of conductivity.
Pure water will not conduct electricity. Water usually conducts electricity
because it is full of impurities, in our case, electrically charged nutrient ions.
The two black dots on the end of a conductivity probe are called electrodes.
When these are placed in a solution, an electrical current passes from one
electrode, through the water to the other electrode and counts the number
of electrically charged ions present. This represents the units measured - EC.
ppm measures parts per million
There are many different scales used for different industries around the world
and for many different reasons! Did you even know there are more than two
scales? The most widely used scales in Hydroponics are the 500 scale, 650
scale and the 700 scale.
What’s the difference?
The ppm 500 scale is based on measuring the KCl or potassium chloride
content of a solution. The ppm 700 is based on measuring the NaCl or
sodium chloride content of a solution. Individual nutrient ions have different
electrical effects! The true ppm of a solution can only be determined by a
chemical analysis. ppm cannot be accurately measured by an EC meter. They
are present on Bluelab products as a conversion guide only. The conversion is
as follows;
2.4 EC x 500 = 1200 ppm (500 scale) or 1200 ppm / 500 = 2.4 EC
2.4 EC x 700 = 1680 ppm (700 scale) or 1680 ppm / 700 = 2.4 EC
If you are wanting to measure your solution in ppm, you will need to know
the following:
• What ppm scale is your meter using?
• Which calibration standard should you use for your meter?
• What ppm scale is my nutrient referring to?
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