An EC / TDS meter tests the electrical conductivity and dissolved solids of water samples or other liquids. Hydroponic gardeners use these meters to determine if they use the right balance of nutrients and buffers. Owners who depend on water and use these meters to make sure their water does not have too high a concentration of minerals or other impurities. The meter gives a reading on its screen after inserting its probes or electrodes in a water sample. You can rely on the TDS reading from the screen or calculate yourself from the CE reading.
1. Calibrate your EC / TDS meter according to the manufacturer’s recommendations.
2. Fill a plastic cup with water or a hydroponic gardening solution. Mix or shake the water with a stirring rod or plastic spoon. Place the probes of your meter in the cup so that they are submerged in the water, but do not touch the sides or the bottom of the cup.
3. Turn on the power and set the dial or dial to the setting for CE playback. Note the result and note if the reading is in millisiemens (mS) or micro siemens (small “u” with a tail followed by a capital S).
4. Set the dial or selector to TDS if you want to use the conversion scale the meter uses to calculate total dissolved solids in the solution. Note the result, which is expressed in ppm (parts per million). Go to step 5 if you want to convert the reading CE to a different scale.
5. Multiply the CE reading you obtained by 700 if it is expressed in millisiemens or by 0.7 if it is expressed in micro siemens to calculate the TDS according to the scale “442” which is used to measure the freshwater. For example, if your meter reads 4000 micro-siemens, you must multiply 4000 by 0.7 for a result of 2,800 ppm, according to the scale of 442. For 4.0 millisiemens, you must multiply by 4.0 700 to get the same, the correct result of 2.800 ppm.
6. Multiply the CE reading you obtained by 500 if it is expressed in millisiemens or by 0.5 if it is expressed in micro siemens to calculate the TDS according to the “NaCl” scale used to measure saltwater and chemical solutions. For example, if your meter reads 4000 micro-siemens, you must multiply 4000 by 0.5 for a result of 2,000 ppm according to the NaCl scale. For 4.0 millisiemens, you have to multiply by 4.0 500 to get the same, the correct result of 2.000 ppm.
7. Multiply the reading you obtained by EC 535 if expressed in millisiemens or 0,535 if it is expressed in micro siemens to calculate the TDS according to the “KCl” scale used in the scientific measurement. For example, if your meter reads 4000 micro-siemens, you must multiply by 4.000 0.535 for a result of 2.140 ppm according to the KCI scale. For 4.0 millisiemens, you have to increase by 4.0 535 to get the same, the correct result of 2.140 ppm.
8. Take additional sample readings before making any decision to correct a chemical imbalance in your hydroponic solutions or adjust the hardness of your freshwater. Check the average of three to five readings against the recommendations for your plants or solutions or the level of hardness in ppm (according to the 442 scales) that you want to achieve for your drinking water.