Understanding EC vs. TDS/PPM, and Why You Should Use EC
Overview of Terminology:
EC stands for Electrical conductivity, which is exactly what it may sound like…it’s a measure of how well a material conducts electricity. This is relevant to your hydroponic garden because hydroponic nutrients are made up primarily of mineral salts, which are a great conductor of electricity. By measuring EC in your hydroponic solution, you are basically measuring the amount of nutrients that are contained in your hydroponic solution.
TDS stands for Total Dissolved Solids, which is also exactly what it may sound like…it’s a measure of how many dissolved solids are in a liquid. This is relevant to your hydroponic garden because hydroponic nutrients become the dissolved solids in your reservoir. The measurement you receive is reported as PPM or ‘Parts Per Million.’ In other words, your TDS meter will spit out a result like ‘100 PPM,’ which means that for every million particles in a solution, 100 are from dissolved solids, and 999,900 are from water.
Reporting:
You can compare measuring EC and PPM to measuring inches and centimeters. In both cases, you are measuring the same thing. In the case of EC and PPM, you are measuring the amount of ‘stuff’ in your water. In the case of inches vs centimeters, you are measuring distance. The numbers will be different, but the meaning will be the same.
In fact, standard meters used for hydroponics always use EC to measure the amount of nutrients in your water. There are two probes in the bottom of your EC meter, and they measure the ease by which electricity is able to move through your water. Then, to report a PPM, the meter does a quick calculation to provide the PPM result.
Why We Prefer to Use Electrical Conductivity (EC):
It’s safest for you to use EC values to measure the nutrients in your hydroponic reservoir. That’s because there is unfortunately more than one way to convert EC to PPM. If your meter measures an EC of 1.0 mS, your meter may report your Total Dissolved Solids as either 500PPM or 700PPM. This is obviously a very big difference, and it’s not always easy to determine which method your meter is using to convert EC to PPM. So, to simplify, we suggest always using EC to measure the nutrients in your hydroponic reservoir. This will give you the most consistent and accurate results, no matter what meter you use for measuring your dissolved nutrients.
Nutrient Chart With Comparative Values:
| EC (mS) | EC (µS) | PPM (500) | PPM (700) |
| 1.0 | 1000 | 500 | 700 |
| 1.5 | 1500 | 750 | 1050 |
| 2.0 | 2000 | 1000 | 1400 |
| 2.5 | 2500 | 1250 | 1750 |
| 3.0 | 3000 | 1500 | 2100 |
| 3.5 | 3500 | 1750 | 2450 |
| 4.0 | 4000 | 2000 | 2800 |
| 4.5 | 4500 | 2250 | 3150 |
| 5.0 | 5000 | 2500 | 3500 |
| 5.5 | 5500 | 2750 | 3850 |
| 6.0 | 6000 | 3000 | 4200 |
| 6.5 | 6500 | 3250 | 4550 |
| 7.0 | 7000 | 3500 | 4900 |
| 7.5 | 7500 | 3750 | 5250 |