So you just got your first hydroponic system and are excited to start growing your own plants. But what is all the fuzz about adding Nutrients and measuring Total Dissolved Solids (TDS) and Electrical Conductivity (EC)? That is how I felt when I first started growing with hydroponics, and it was confusing, to say the least.

Don’t worry though! In this article, we will explain what TDS and EC are, why they’re important for your hydroponic system, and how you can use them to provide your plants with a nutrient-rich water solution.

TDS and EC in hydroponics, measuring the concentration of dissolved solids and electrical conductivity of the nutrient solution. TDS is measured using a conductivity meter, while EC measures the solution’s ability to conduct electricity. Monitoring these parameters of dissolved solids like minerals and salts ensures, that plants receive adequate nutrients and prevents imbalances.

Hydroponic Nutrient

When growing hydroponically you are growing plants without soil. Because you are not using soil, all the nutrients your plants need come from the water solution, in which you add a hydroponic nutrient. The components of this nutrient can be divided into minerals and trace elements.

Nutrients are essential for healthy and strong hydroponic plants to grow and thrive. Nutrients come in various forms, such as macronutrients:

nitrogen, phosphorus, and potassium

and micronutrients such as:

calcium, magnesium, and sulfur

Together they provide the necessary minerals to fuel photosynthesis and other plant metabolic processes.

To do this, it’s essential to understand TDS and EC, two key metrics used to measure the quality of a nutrient solution.

Total Dissolved Solids (TDS)

Total Dissolved Solids (TDS) are the total amount of dissolved minerals, salts, metals, and anions present in the solution you are measuring.

Basically, it’s a measure of all the minerals and other particles that are suspended in the water solution. Think of TDS as the total amount of “stuff” dissolved in your water. The higher the TDS, the more “stuff” there is in your water.

However “Stuff”, does not include solids, like pebbles or rock wool suspended in your solution, it only includes dissolved solids.

How to Measure TDS

The accurate way to measure TDS is by taking a sample of water and evaporating it until there is no more liquid left and weighing the remaining material.

However, that is a very long process of sending samples to a lab and waiting for results, and not really suitable for the everyday gardener. For the purpose of hydroponics, there are easier methods such as using a TDS meter.

But Before we can talk about that, we need to understand what EC (electrical conductivity) is.

Electrical Conductivity (EC)

EC is a measure of the ability of water to conduct electricity. EC is measured in mS/cm. mS stands for millisiemens and cm stands for centimeter, so it’s a measure of how much current can pass through one centimeter of water in a given amount of time.

It’s related to TDS because it measures the number of ions dissolved in a solution, which are usually minerals and salts.

In general terms, EC measures how many particles in your water can conduct electricity.

Basically, all salts are made up of two different elements, like sodium and chloride, and when they dissolved in water the atoms become charged ions. So if you have pure clean water like RO (reverse osmosis) or distilled water, then the EC will be almost zero because there are no charged ions in that water.

But when you add nutrients (salts) to your solution and dissolve them, they contribute with their charged atoms, raising the electrical conductivity (EC) number.

So a TDS meter measures the total number of particles in a solution, and an EC meter is used to measure how many of those particles can conduct electricity

Tds vs EC Meter

But as we discussed earlier, the only way to get the exact amount of TDS is by evaporating the water and measuring the leftovers.

So it’s not possible to measure TDS accurately with a TDS meter, but that’s where EC comes into play!

EC and TDS are closely related. A TDS meter is actually just an EC meter with a built-in conversion factor. So the readings given by the TDS meter are actually converted from EC readings to approximate TDS readings by using a ppm scaling factor.

This means that if you know the EC of your water solution, you can get an estimate of how much dissolved minerals and salts are present in it.

What is PPM (parts per million)

So if you looked at the readings of most TDS meters or back on the feeding chart of your nutrients, you may have seen that they are measured in “PPM” (parts per million).

This is a measure of how many ‘parts’ of a substance are dissolved in 1 million parts of water. So if you have a reading of 1000 ppm in your solution then it means that there are 1000 parts of dissolved solids in 1 million parts of water.

This is the same as saying that there are 0.1 grams (1000 milligrams) of dissolved solution in 1000 liters (1 million mL) of water.

Conductivity Scales & EC/ppm conversion

Now here comes the tricky part of using a TDS meter to measure ppm.

When calculating the ppm from EC readings, it’s done by using a Conductivity Scale. This scale is simply a conversion factor between EC and PPM. But it’s important to know that there are different scales used for different industries and countries to express the concentration.

In hydroponics, you will typically encounter three widely-used ppm scales: ppm500 and ppm700.

For example, some scales are based on a conversion factor of 500 to equate EC and PPM, while other scales use 700 or even 800.

So let’s say that we want to calculate the ppm of a water solution with an EC reading of 2.0 mS/cm and we are using the ppm500 scale.

In this case, the calculation would be as follows:

2.0 mS/cm (EC reading) x 500 (scale factor) = 1000 ppm.

This means that the water solution contains 1000 parts of dissolved solids in 1 million parts of water, according to the ppm500 scale.

So if your TDS meter is calibrated to one scale, but you are using nutrients from a manufacturer with a different scale, then the readings you get from the meter will be inaccurate.

you can also try using this EC & ppm conversion tool I have on my site

Should I Use EC or Tds to Measure Nutrient Concentration?

So, which one should you use when measuring the nutrient concentration of your water solution: EC or TDS?

Ultimately, the choice between EC and ppm may come down to personal preference. In some countries, TDS is more widely used and accepted than EC. However, it is important to remember that the readings you get from a TDS meter are converted EC readings and only an estimate of the true nutrient concentration in your water solution.

The most accurate way to measure nutrients is still with an Evaporation Test or Refractometer. But if you want a simple and quick way to get an approximate measure of the nutrient concentration, then either EC or TDS readings are sufficient.

I myself prefer to measure the EC of my water solution with a EC meter from Blue Lab. This way I can be sure that I’m getting precise readings, no matter which ppm scale my nutrient manufacturer uses, and ppm from a TDS meter are just calculated EC anyway.

Understand TDS and EC in Mixing Nutrient Solutions

Now that we have learned the basics of EC and TDS, it’s time to apply what we know in our hydroponic garden.

When growing plants with hydroponics, you want to use EC and/or TDS readings to monitor the nutrient concentration in your water solution. This will help ensure that your plants are getting all the nutrients (salts and minerals) they need for healthy growth.

Different plants need different levels of nutrients. Some plants like tomatoes and peppers need a higher nutrient concentration than lettuces and herbs, so it’s important to adjust your EC/ppm level according to the type of plant you’re growing.

Let’s take a look at the process of mixing the nutrient solution and adding it to your hydroponic system. Whether you choose to mix your nutrient solution with TDS or EC, the process remains the same:

Filling your reservoir

Start by filling your reservoir with fresh clean water about 68 F. your tap water will most likely already have some TDS in it due to the minerals it contains. A range between 200-300 ppm is considered safe but depends on your country. Many growers use reverse osmosis systems to filter water to almost 0 ppm, then they have complete control of the TDS from the beginning.

Check your plants preferred EC/ppm range:

If you do not know your plant’s preferred EC/ppm range, now it’s time to check. Below I have a table with some of the most common crop types.

Plant	pH	EC	PPM
Basil	5.5-6.5	1.0-1.6	700-1120
Bean (Common)	6.0-6.0	1.8-2.4	1400-2800
Bean (Broad)	6.0-6.5	1.8-2.4	1400-1800
Bell Peppers	6.0-6.7	1.8-2.8	1400-2000
Broccoli	6.0-6.5	2.8-3.5	1960-2450
Brussell Sprouts	6.5-7.5	2.5-3.0	1750-2100
Cabbage	6.5-7.0	2.5-3.0	1750-2100
Cauliflower	6.0-7.0	0.5-2.0	1050-1400
Celery	6.3-6.7	1.8-2.4	1260-1680
Chives	6.0-6.5	1.8-2.4	1260-1680
Cilantro	6.5 – 6.7	1.3-1.8	910-1260
Cucumber	5.8-6.0	1.8-3.0	1190-1750
Eggplant	5.5-6.5	2.5-3.5	1750-2450
Lavender	6.4-6.8	1.0-1.4	700-980
Lemon Balm	5.5-6.5	1.0-1.6	700-1120
Lettuce	5.5-6.5	0.8-1.2	560-840
Melon	5.5-6.0	2.0-2.5	1400-1750
Mint	5.5-6.0	2.0-2.4	1400-1680
Pak-choi	7	1.5-2.0	1050-1400
Parsley	5.5-6.0	0.8-1.8	560-1260
Pea	6.0-7.0	0.8-1.8	580-1260
Peas (Sugar)	6.0-6.8	0.8-1.9	580-1261
Peppers (Bell)	6.0-6.5	2.0-2.5	1400-1750
Peppers (Hot)	6.0-6.5	2.0-3.5	1400-2450
Pumpkin	5.5-7.5	1.8-2.4	1260-1680
Sage	5.5-6.5	1.0-1.6	700-1120
Spinach	5.5-6.6	1.8-2.3	1260-1610
Squash	5.0-6.5	1.8-2.4	1260-1680
Sunflower	5.5-6.5	1.2-1.8	840-1260
Strawberries	5.0-5.5	1.0-1.4	500-700
Swiss Chard	6.0-6.5	1.8-2.3	1260-1610
Thyme	5.5-7.0	0.8-1.6	560-1120
Tomato	5.5-6.5	2.0-5.0	1400-3500
Watercress	6.5-6.8	0.4-1.8	280-1260
Watermelon	5.8	1.5-2.4	1050-1680
Zucchini	6.0	1.8-2.4	1260-1680

EC/ppm and pH chartchart

Manufacturer’s feeding chart

Now it’s time to look at your manufacturer’s instructions for the nutrients you use. Most likely there will be a chart that explains the recommended EC/ppm range for different stages of growth. For example, I’m using Tera Aquatica’s 3-part nutrition solution, which recommends an EC of 1.3-1.8 for the growing stage (see chart below).

Measure out the nutrients mix

Measure out each of the 3 nutrients (grow, micro, bloom) according to the doses given by the chart. This can be done with a syringe, pipette, or measuring spoons. and add it to the reservoir. Add each one at a time and stir thoroughly.

Check EC/ppm

Once you have measured out and added all the nutrients, wait 5 minutes for them to dissolve into the water, then measure the EC/ppm of your nutrient solution with a meter. Depending on what you’re growing, adjust the concentration of nutrients if needed by adding more nutrient or diluting it with clean fresh water.

Check pH

Before you are finished remember to check your PH level with a pH meter and adjust if necessary, most nutrients and plants work best at a pH of 5.5-6.5, but again, check your manufacturer’s instructions and plant requirements.

Now you are ready to fill your system and start growing!

Conclusion

Overall, Total Dissolved Solids (TDS) and Electrical Conductivity (EC) are two important concepts that you need to understand when providing your plants with a nutrient-rich water solution. With the right tools, like an EC meter or TDS meter, and by understanding the specific needs of each plant species, you can measure and adjust the concentration of nutrients in order to ensure healthy growth for all types of crops. By following these steps carefully and consistently monitoring pH levels as well as dissolved solids content in your hydroponic system’s reservoir, you will be able to provide optimal conditions for growing lush and vibrant plants!

Happy gardening! ; )

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Hydroponic Nutrient Management: TDS and EC Explained