What are pH, EC, TDS, and PPM
If you’re new to hydroponics and have NO clue what all of the terminology means, this article is for you.
Even if you’re an intermediate grower and want to know what EC is, what TDS means, which you should use, and how it all connects to pH, make some time to read the article or watch this one today.
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The truth is that EC or electrical conductivity is the purest way to measure your nutrient concentration. TDS or total dissolved solids is a calculation based on EC that meters perform internally.
TDS is measured in PPM, or parts per million and the calculation can vary based on the conversion factor.
This is why you must know the conversion factor your meter is using if you’re using TDS. Or you can simply switch to using EC and never have to worry about it again!
For the proper development of plants, it is necessary to use solutions with an optimal set of macro- and microelements. But how to control the nutrient content of the solution?
What are pH, EC, TDS, and PPM and How Are They Connected?
TDS ( Total Dissolved Solids
TDS , the total dissolved solids content, is a measure of the combined content of all inorganic and organic matter contained in a liquid.
- A TDS meter (salinometer) is used to measure the concentration of dissolved solids in a solution .
- A TDS meter usually displays concentration in parts per million ( ppm or mg / L).
The only accurate method for measuring TDS is to evaporate the water and weigh the dry matter. This is difficult and time consuming, so TDS meters are used as a cheap method, which estimate the TDS level by measuring the EC of the water.
Each TDS meter is essentially an EC meter. The TDS meter measures EC and then converts it to TDS using an internal correction factor. TDS meters from different manufacturers may have different conversion factors.
EC ( Electrical Conductivity )
EC – electrical conductivity meter. It is widely used in hydroponics, aquaculture to monitor the amount of salt or impurities in solution.
Electrical conductivity is the ability of a solution to conduct electrical current. EC is measured in µS / cm (µS / cm or microsiemens per centimeter) or mS / cm (mS / cm – millisiemens per cm). Conversion formula: 1 mS / cm = µS / cm: 1000.
An EC meter (conductometer) is used to measure electrical conductivity.
Conductivity meters (EC meters) are preferred by commercial manufacturers because they provide a more accurate estimate of the concentration of the nutrient solution, while the TDS measurement is a “rough” estimate.
This video is sponsored by Apera Instruments, makers of water and soil testing probes and meters. They kindly donated the PH20 and PC60 meters for me to make this video.
EC in nutrient solution
The conductivity of a solution is highly temperature dependent. Therefore, it is important to measure EC at the temperature at which the meter was calibrated. But, now sold conductometers with a built-in sensor for automatic temperature compensation.
Likewise, EC should always be measured at constant pH. By measuring the EC at pH 5 and at pH 7, you will get completely different values, since the ions that determine pH have a very large influence on the EC value.
In a nutrient solution used in a hydroponic system, the EC will change over time. This is due to the different rates of absorption of water and nutrients by the plant. For example, at high air temperatures, transpiration (evaporation of water by the plant) increases, and the plant absorbs more water from the solution than salts.
This extra water evaporates from the leaves and cools the plant. Accordingly, the EC of the solution increases. Therefore, in hot weather, it is necessary to reduce the concentration of the solution and more often to supply the solution to the root zone.
So why do we need to measure EC?
We need to measure EC in order to monitor the total nutrient content of the solution. Electrical conductivity can show you that a solution has lost its nutritional value or that the amount of water has decreased due to evaporation, provided the pH remains unchanged.
If the EC value has increased, water can be added to reduce the salt concentration.
If the EC value has dropped significantly (more than 30% of the original value), then your solution has changed significantly in composition and needs to be replaced with a new one.
You can’t add nutrients because you don’t know which nutrients the plant has been using and which are not. Of course, you can always do an expensive chemical analysis, but the cheapest and easiest way is to prepare a new solution.
If, nevertheless, you decide to add at your own peril and risk elements to increase the EC, then keep in mind that they are most likely to cause changes in the EC in the solution – N and K. When replenishing the solution, trace elements and phosphorus should never be added
Required concentration of solution
Plants are generally classified into three groups requiring high, medium and low EC.
Greens, lettuce, beans and most herbs require a low EC of 0.7 to 1.5 mS / cm (mS / cm) in winter and 1.5 to 1.8 mS / cm (mS / cm) in summer.
Cucumbers, melons , many ornamental plants and some types of cabbage prefer an average EC of about 1.6-1.8 mS / cm (mS / cm) in summer and 1.8-2.2 mS / cm (mS / cm) in winter. period.
Tomatoes, peppers and eggplants prefer higher conductivity, in the order of 2.5 – 3.6 mS / cm (mS / cm) in summer and 3.6 to 5.0 mS / cm (mS / cm) in winter.