All Hydro 101

Understanding EC/PPM: Q&A with Blue Lab

We all understand the importance of applying nutrients at the correct strength and the appropriate time to achieve successful crop production. This is why we utilize tools like EC/PPM meters to accurately measure these levels. To understand how these tools work, and to better grasp what happens when we measuring a nutrient solution, we spoke with Cindy from Bluelab USA and asked her some of the more common questions we encounter.

What is the difference between EC, PPM, and TDS?

  • EC = Electrical Conductivity
  • PPM = Parts Per Million
  • TDS = Total Dissolved Solids
  • All meters/pens measure EC. The EC measurement is then converted to PPM or TDS using the following formulas;
  • EC X 700 = PPM 700; Example: 1.00 EC = 700 ppm.
  • Or 1.3 EC x 700 = 910 ppm
  • EC X 500 = TDS (or PPM 500); Example: 1.00 EC = 500 ppm.
  • Or 1.3 EC x 500 = 650 ppm

PPM is a way of expressing very dilute concentrations of substances. Just as percent means, out of a hundred, parts per million (PPM) means out of a million.

How does my EC/PPM meter measure my nutrient solution? 

All meters and pens, measure the Electrical Conductivity (EC) of your nutrient solution. Pure water, like reverse osmosis (RO) water, has no conductivity. This is why, when you place an EC or PPM probe into pure water, it does not register on the meter.  When you add nutrient solution it conducts electricity.  The more nutrient solution you add, the higher the conductivity level, which causes the reading on your device to rise.


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Which PPM/TDS scale should I use? 

It depends on which “scale” your nutrient company uses during manufacturing. For example, Botanicare utilizes the 700 PPM scale. All Bluelab meters/pens read EC, PPM 500 (TDS), or PPM 700, allowing you to match your meter to your nutrient scale.

Is one scale better than another? 

EC is the only true measurement and does not have to be converted so EC is always the same. If you use PPM/TDS, which is most popular in the US, you need to make sure your meter is set to the same scale your nutrient is using, since there are 2 different conversion formulas. In short, it’s best to use the scale that your nutrient manufacturer recommends.

Which inputs increase PPM? Do minerals (salts), amino acids, humic/fulvic acids, and trace minerals also raise PPM?

Any mineral, trace mineral, or input that is able to dissolve (disassociate into ionic form) into a solution can be measured. Amino acids and other organic acids such as humic and fulvic with the ability to
be present in ionic form will also contribute to the EC/PPM measurement.

Are there any minerals/inputs that my meter does not read?

No. Provided they are disassociated into ionic form, any and all minerals and their charged ions will contribute to the overall electrical conductivity reading, which raises your total EC/PPM.

Does my meter work with fully organic nutrients?

No. Your meter will not read a “completely” organic nutrient solution. It is important to note that, when supplied to plants in an organic form, nutrients still must cycle (break down) into their inorganic form before becoming available for plants to uptake.

Continued in NPK: A simple guide