Marijuana (Cannabis)

Measuring Hydroponic Nutrient Solution - EC, TDS, PPM

For hydroponic growers, an EC or TDS meter will measure how strong a nutrient solution is. A larger EC or TDS meter reading indicates an increase in the concentration of nutrient in a nutrient solution, when compared to a lower reading.

EC and TDS meters measure the amount of N-P-K, secondary nutrients, trace elements, as well as any impurities that are dissolved in water. For cannabis growing applications impurities should be kept as low as possible.

If you start with reverse osmosis or distilled water the amount of impurities will be next to nothing. When measured with an EC or TDS meter, the reading will be near 0. Unless filtered, well and tap water will contain impurities.

EC stands for electrical conductivity. EC meters are a method of measuring the amount of dissolved solids in nutrient solution. More solids will conduct electricity more efficiently, resulting in a higher reading.

Depending on the meter, EC can be measured on several different scales, including:
A) µS/cm (microSiemens per centimeter)
B) cf (conductivity factor)
C) mS/cm (milliSiemens per centimeter).

The scale the different EC readings are measured on is similar to those on a volt meter that can measure millivolts (mv), volts (v), kilovolts (kv) ...

The difference is instead of letting you view readings of several different scales, some EC meters only allow you to take a reading on one or two different scales.

If you have an EC meter that reads in µS/cm you can compare your measurement with someone that had a reading in cf or mS/cm by moving the decimal place.
100 µS = 1.0 cf = 0.1 mS
200 µS = 2.0 cf = 0.2 mS
400 µS = 4.0 cf = 0.4 mS
600 µS = 6.0 cf = 0.6 mS
800 µS = 8.0 cf = 0.8 mS
1000 µS = 10.0 cf = 1 mS
1400 µS = 14.0 cf = 1.4 mS

TDS stands for total dissolved solids, TDS meters are another method of measuring the amount of dissolved solids in nutrient solution.

TDS meters display a reading in parts per million, ppm. To get a reading, they take measurements like an EC meter, then convert to ppm based on a conversion factor according to several different standards.

Different TDS standards include:
NaCl conversion (NaCl)
442 conversion (442)
KCl conversion (KCl).

NaCl conversion works out to approximately: EC in µS divided by 2. So 1000 µS is equal to about 500 ppm (NaCl).

To compare TDS meter readings with other people, you will need to know the conversion standard of both meters, if they are the same you can compare directly.

If TDS meters are calibrated to different standards, you will need find out what standard each meter is calibrated to and then find a conversion chart or formula, to convert between the two different standards.

To convert between EC and TDS (NaCl):
100 µS = 1.0 cf = 0.1 mS = 50 ppm (NaCl).
200 µS = 2.0 cf = 0.2 mS = 100 ppm (NaCl).
400 µS = 4.0 cf = 0.4 mS = 200 ppm (NaCl).
600 µS = 6.0 cf = 0.6 mS = 300 ppm (NaCl).
800 µS = 8.0 cf = 0.8 mS = 400 ppm (NaCl).
1000 µS = 10.0 cf = 1 mS = 500 ppm (NaCl).
1400 µS = 14.0 cf = 1.4 mS = 700 ppm (NaCl).

Part 01) See the full hydroponic marijuana nutrient article here.
Part 02) Nutrients and hydroponic marijuana introduction here.
Part 03) Water and hydroponic nutrients here.
Part 04) Preparing hydroponic nutrients here.
Part 05) Measuring hydroponic nutrient solution - EC, TDS, PPM here.
Part 06) Hydroponic nutrient strength here.
Part 07) Hydroponic nutrient solution temperature here.
Part 08) Flushing or leeching hydroponic nutrient here.
Part 09) Amount of water for hydroponic marijuana plants here.
Part 10) Hydroponic nutrient list of materials here.