One of the most important aspects of successful hydroponics is nutrient management. Nutrient solutions are made up of dissolved solids from soluble chemical compounds that are specifically made for greenhouse or hydroponic uses. Generally, the dry (yet soluble) compounds are mixed appropriately to form “stock solutions” or concentrated fertilizer solutions. The stock solutions are then added to the water source to make up the nutrient solution for the crop. Plants grown hydroponically are completely dependent on the nutrient solution to supply proper amounts of “food” for growth and development. How do you know if you are supplying enough nutrient solution? In short, the grower should know their plant, know how many parts per million (ppm) of each element that plant needs for growth and development, and routinely check the nutrient solution’s Total Dissolved Solids (TDS) or Electrical Conductivity (EC). To do this, growers use TDS and/or EC meters.
Total Dissolved Solids or TDS meters measure the ppm of a solution. They are simple to use and can be less cumbersome to maintain if a grower is new to hydroponics. TDS meters are generally less expensive than EC meters and easily replaceable if broken. If a grower is small to mid-size, has entry-level employees, and has a limited budget for monitoring equipment, a TDS may be the best option. The caveat of a TDS meter is converting a ppm measurement to EC. Generally, the packaging of a TDS meter will include a small chart, that is, a conversion table to convert ppm to microelements (μS/cm2) or millisiemens (mS/cm2). The conversion factor will heavily depend on the type of TDS meter and the country in which the measurement is taken. There is a change in the way they are made nowadays. The increased demand for TDS meters has enabled makers to include EC readings in some models, leaving accuracy as the major unknown in cheap models.
Electrical Conductivity or EC meters can measure a plethora of things from pH to EC to the temperature of the solution. This meter is more typically used in laboratories and grow operations that require precision. EC meters are expensive; averaging between $100 and $200. Handheld devices can get more expensive depending on the precision demands. These more scientific devices also require routine calibration that calls for multiple types of solutions which adds to the overall expense. It is advantageous, however, to have the ability to take multiple types of extremely accurate measurements with one device. Generally, EC meters also take readings in ppm if so desired.
Which meter is best? Well, this is completely dependent on the grower and the situation. Enthusiasts and small growers may prefer the TDS due to the expense and availability of the equipment. Growers involved in research and development or commercial operations in need of precise data are more likely to spare no expense. The more important takeaway is to routinely check the nutrient solution, no matter what meter is used.
-Inexpensive -Reads soluble salt levels in ppms
-Not as accurate as some EC meters -Requires a conversion factor to get μS/cm2 reading
-Accurate readings in μS/cm2 -Able to take multiple measurements at one time (μS/cm2, pH, ppm, & temperature)
-Expensive -Calibration requires multiple solutions
Dutch Master Nutrients. “PPM VS EC.” Dutch Master Nutrients, Dutch Master Nutrients, 4 May 2018, https://dutchmasternutrients.com/growers-guide/ppm-vs-ec/.
“EC and TDS for Plants and Hydroponics: HTG Supply Hydroponics & Grow Lights.” HTG Supply Products, https://www.htgsupply.com/informationcenter/talking-shop/ec-and-tds-for-plants-and-hydroponics/.
Scherer, Tom. “North Dakota State University.” Using Electrical Conductivity and Total Dissolved Solids Meters to Field Test Water Quality - Publications, North Dakota State University, https://www.ag.ndsu.edu/publications/environment-natural-resources/using-electrical-conductivity-and-total-dissolved-solids-meters-to-field-test-water-quality.