TDS, EC, and PPM explained in briefFast growth and high yields are the main goals in aqua and hydroponics. This success is decided by many details.
As a grower, you need to find the comfort zone of nutrient strength so that your plants can grow properly. If you add too many nutrients, the plants will be affected by a severe case of nutrient burn. Too few nutrients will cause the plant to wither or produce only a low yield.
Do not wait for the symptoms to appear. Prevention is better in hydroponics than damage or even total loss.
Important here: check the nutrient solution regularly. To get a complete picture, you need to analyse certain physical and chemical properties of your nutrient solution.
Here you will come across terms like TDS, EC and PPM. These terms revolve around the concentration of dissolved nutrients - more precisely, the parts of the nutrient solution that are dissolved in the water, through which the salinity can be determined. For more details on electrical conductance, see Wikipedia.
Another hurdle is that malformations or deficiencies can easily be misinterpreted. Here is a brief overview of the nutrients that can get in each other's way if they are wrongly concentrated and in the worst case can even completely block nutrient uptake.
Before we get down to business, here's what these abbreviations stand for:
TDS: Totally Dissolved Solids.
EC: Electrical Conductivity PPM: Parts per Million (Parts per MIllion)
What are completely dissolved solids (TDS)?Water is described as a universal solvent capable of dissolving a wide range of organic and inorganic compounds and minerals. The TDS value of water measures the total amount of minerals dissolved in the water. The solids are dissolved either in the form of ions, molecules or tiny micro-granular particles that cannot be filtered out with normal filters (size of two micrometres).
This measurement is usually used in the context of fresh water. For salt water, the term "salinity" is used, which basically says the same thing. The TDS value is a measure of water quality, but not a direct indication of pollution. It provides information about the amount of dissolved solids, not about the dissolved substances themselves. All water, including drinking water, contains various minerals and compounds in solution. Tap water contains calcium, magnesium and of course chlorine ions. Bottled mineral water contains even more dissolved minerals than tap water.
The higher the TDS value of a water sample, the lower its suitability for various purposes. The dissolved solids in water are measured in ppm. As a guide, here are some TDS values that occur in nature:
Freshwater - TDS less than 1000ppm (WHO standards).
Brackish water - TDS up to 5000ppm Saltwater - TDS between 15,000 - 30,000 Seawater - TDS between 30,000 and 40,000ppm Brine - TDS above 40,000ppm In the context of hydroponics, the TDS value gives you a clear idea of the strength or concentration of your nutrient solution. This will give you accurate information about the amount of nutrients your plants are receiving from the water.
What is electrical conductivity (EC)?
Water is a good conductor of electricity, which is why many electrocution accidents occur in bathrooms. But did you know that pure water is an excellent insulator! Pure water, i.e. H2O without any other minerals or molecules dissolved in it, does not conduct electricity. However, as soon as mineral salts are dissolved in it, the electrical properties of water change drastically. And since water is very corrosive, it easily dissolves many minerals, salts and compounds. For this reason, all waters found in our environment prove to be good conductors of electric current.
Salts form charged particles called ions in water. These include positively charged cations (which consist of metals) and negatively charged anions (which consist of non-metals).
Even a small amount of dissolved salts is enough to drastically increase the electrical conductivity of the water. And the more salts dissolved in the water, the higher the number of ions and the higher the electrical conductivity of the water.
How does this affect hydroponics? Well, the vast majority of nutrients used in hydroponics contain salts such as nitrates and phosphates. So when you add nutrients, the EC value of the water increases. If you measure the EC value, you can get a pretty good idea of the nutrient concentration in your water.
The EC value is measured with two interconnected units. These are MilliSiemens and MicroSiemens. For orientation: 1 MilliSiemens = 1000 MicroSiemens.
A quick look at parts per million (PPM).
We have already mentioned ppm when explaining TDS. In chemistry, ppm is a common value used to describe substances dissolved in minute amounts in air, water and soil. PPM is basically analogous to a percentage. Just as a percent means one in a hundred, a ppm is equivalent to one part in a million of something.
You will often see ppm used to measure the level of pollution in water and air. PPM is easier to understand if you use the metric system. For example, to achieve a salt concentration of 1ppm in water, you need to dissolve 1 milligram of salt in 1 litre of water. (or 1 gram in 10,000 litres!)
What is the relationship between TDS and EC?
As you know by now, the TDS value gives you an accurate idea of the amount of dissolved solids in a water sample. And the EC value gives you a clear picture of the salt concentration in a water sample.
In the environment, there is often only a partial correlation between electrical conductivity and TDS value. In a hydroponic growing system, however, the relationship is more direct for several reasons.
Take, for example, the water in a lake or well. It contains a significant amount of dissolved minerals, salts and other organic and inorganic compounds. Only a fraction of the total TDS, namely the salts, affect the EC.
However, hydroponic growers try to use higher quality water for their plants whenever possible. And almost all components of hydroponic nutrient mixtures are in the form of easily soluble salts.
Therefore, EC and TDS values in hydroponic nutrient solutions are more directly related due to the high proportion of dissolved salts. Your main goal as a grower is to get an accurate estimate of the concentration of your nutrient solution. Both TDS and EC values are a viable way to obtain this information.
If you know one value, you can calculate the other with the help of a so-called conversion factor.
Not all salts have the same electrical conductivity. If one salt increases the EC value of the water by one microsiemens at a TDS value of 1500 ppm, another salt may only need 1000 ppm to achieve the same result. So depending on the salt, you will need a suitable conversion factor to get an accurate TDS value. This factor is normally between 0.5 and 0.8, so the basic formula for calculating TDS or EC is
TDS = ke*EC (where KE is the conversion factor).
Another important factor that can affect the above equation is the temperature of the water. The EC value of a salt solution can fluctuate with temperature changes. The higher the temperature, the better the electrical conductivity.
How to measure TDS and EC
There are several ways to measure both TDS and EC. For example, one method commonly used in laboratories is to evaporate the liquid and then measure the residue.
However, from the perspective of the average hydroponic grower/hobbyist, advanced laboratory measurements are not applicable. Instead, most growers use simple handheld meters to measure either TDS or EC. You can use either an EC meter or a TDS meter.
A TDS meter is actually nothing more than an EC meter that has a built-in conversion system. This
system is programmed to use a specific Ke factor to get the result in ppm or mg/L instead of milliSiemens.
But here is a fundamental problem: some TDS meters use a conversion factor of 442, which gives the EC value for a mixture of 4 parts sodium sulphate, 4 parts sodium bicarbonate and 2 parts sodium chloride. The formula for the conversion is 700 x EC in milliSiemens.
Others use a simple sodium chloride conversion factor, which is considered by some to be closer to the EC of a hydroponic mixture. The formula here is 500 x EC in millisiemens.
So depending on the conversion factor used, you get different results with a variation of about 600ppm. That is a wide range for hydroponics. So how do you know if you have the right measurement?
The easiest way is to stick to the EC measurement. However, if you must use TDS, check the source of information. If a book or nutrient mixing guide gives the PPM value, it will usually also give the conversion factor used.
Use this information to calculate the exact final value. In the USA, 500 or 650 ke is commonly used, while 700 ke is preferred in the UK and Europe.
Control of EC/TDS in nutrient solutions
Measuring, calculating and determining the correct EC or TDS value is the difficult part. Dealing with these values, on the other hand, is deceptively easy!
The most important thing is to follow the recommended nutrient values, either in MilliSiemens or PPM. If you are using a commercial nutrient mix, this will be clearly stated on the label.
If the EC level is too low, add more nutrients, and if it is higher than the recommended levels, add more water. That's it.
Remember that these are concentrated mixtures and that a small amount is often enough. But with practice you will soon get the hang of it. Different hydroponics have different PPM values.
Here you will find the Ec and PPM table of some popular vegetables. TO_DO
Data of the main elements in mg/L (ppm)
So knowing the ppm content of each mineral in the solution is the most accurate way to determine the quality of the nutrient solution. However, this requires a detailed test, which is not cheap and takes some time. For this reason it should be done in a commercial production. For hobby gardeners it is not convenient and cheap.
They often measure the ppm value of the nutrient solution and observe the condition of the water and the plants to guess which nutrients the plants need. Then they add the appropriate minerals.
Conclusion
Every hydroponic grower should have an EC / PPM / TDS meter. This takes the guesswork out of the critical process of plant nutrition - at least in large part. To a beginner, EC and TDS may seem too complicated. But once you get the basics down, you'll see that it's simpler than it looks. The biggest confusion comes from the different conversion factors. Unfortunately, there is not much you can do about this, as different salts have different conversion factors. If you want the most accurate measurements, e.g. for advanced or experimental cropping systems, you need to have a lab test done to get the accuracy you need. This is what we offer you here.
But for beginners and hobby growers, EC meters are more than enough.
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