Hydroponics Conductivity and Total Dissolved Solids

Electrical Conductivity (EC) is a measurement of the electrical current generated by the ions in a substance and is expressed in units of milliSiemens per centimeter (mS/cm). Since the relationship between the dissolved ions and conductivity in a solution is known, a conductivity measurement can be used to estimate Total Dissolved Solids (TDS) based on solids being predominantly ionic in nature. In order to estimate the TDS of a solution, a conversion factor (CF) is used to convert microSiemens per centimeter to parts per million (ppm). For weak ionic strength solutions such as fertilizers, a conversion factor of 0.7 is used. For example, a EC reading of 1000 µS/cm (1 mS/cm) can be converted to ppm by multiplying 1000 µS/cm by a conversion factor of 0.7 resulting in 700 ppm (TDS).

Knowing the EC and TDS of a nutrient solution are vitally important in hydroponics since they are used to determine nutrient strength. The EC and TDS of a solution relates to how much nutrient is dissolved in a solution. Therefore, low EC and TDS measurements are usually indicative of low nutrient concentrations when external factors such as, temperature and solution viscosity are kept constant. Due to constant water uptake by plant roots and certain nutrients being favored over others, nutrient imbalances can occur and result in toxic nutrient levels. Without a regulated supply of proper nutrients, plants cannot thrive. Dependent on the plant growth phase, plants usually require a TDS between 200 and 1600 ppm.

It is also important to note that these measurements represent the total nutrients in a solutions and do not specifically indicate the concentration of each individual nutrient. Ion Selective Electrodes can be used as a method to measure the concentration of individual nutrients or ions in a solution.

Testing and adjustment of fertilizer concentration by conductivity or total dissolved solids measurement is a method to maintain the optimal range for your plants growth. Hanna offers a wide range of equipment and accessories to measure, montor, and control the EC/TDS of a nutrient solution.


Portable Meters

A variety of portable meters are available to measure EC/TDS. Many portable meters are made specifically for the hydroponics market. These meters include multiparameter versions that can measure pH in addition to conductivity and/or TDS. Most meters allow for changing of the conversion factor for EC readings to TDS ones.




A variety of testers are available including a version that allows for the direct conductivity measurements in soiless media like rockwool. A direct measurement is an ideal way to trend the build up of salts in the media.




The monitoring & control of nutrient solutions is critical to successful propagation and optimization of plant growth. Different plant species have an optimal tolerance to nutrient solutions.

Monitors offer the ability to continuously measure and display conductivity or total dissolved solids. Multiparameter versions are also available that can also display pH.



Benchtop Meters

Benchtop meters are available for conductivity and total dissolved measurements. This category also included multiparameter versions.





In this category are the replacement EC/TDS probes for the hydroponic meters . Also included are versions for the multiparameter meters.


Calibration Solutions

In this category are conductivity and total dissolved solids calibration standards including our GroLine versions that are supplied complete with a certificate of analysis. The EC/TDS calibration standards are available in a variety of sizes from single use sachets to bottles.

Also included in this category are the Quick Cal solutions used with some of the hydroponic EC/TDS meters. These solutions are formulated for single point calibration of both pH and EC.




Accessories include shockproof rubber boots used with the portable meters. These boots give additional protection from accidental drops and provide for a more tactile feel when holding the meter.


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