Electrical Conductivity (EC) is the measurement of your water's ability to conduct an electrical current, which tells you the exact concentration of nutrients dissolved in your reservoir.
Pure water is a poor conductor of electricity. However, hydroponic fertilisers are made of mineral salts (like potassium, calcium, and nitrate). When these salts dissolve in water, they split into charged ions that allow electricity to flow. More mineral salts in the water mean a stronger electrical current, resulting in a higher EC reading.
EC vs. PPM: What is the Difference?
You will often see nutrient levels measured in either EC or PPM (Parts Per Million). They measure the exact same thing, but use different scales:
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EC (Electrical Conductivity): The universal scientific standard. It is measured in milliSiemens per centimetre (mS/cm) or microSiemens per centimetre (µS/cm). It remains identical on every digital meter worldwide.
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PPM (Parts Per Million): A calculated estimate of total dissolved solids. Digital meters measure the EC first, then multiply that number by a conversion factor (either a 500 scale or a 700 scale) to guess the PPM. Because different brands use different scales, PPM can be confusing and misleading. Always use EC if you want to avoid math errors.
Why EC Matters for Your Plants
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If the EC is too low: Your plants are starving. They will grow slowly, look pale, and produce weak yields.
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If the EC is too high: The water is too salty. This creates osmotic pressure that prevents roots from drinking water, causing "nutrient burn" (dry, crispy, brown leaf tips) and eventual root death.
How to Test Your EC in 4 Steps
To test the Electrical Conductivity (EC) of your hydroponic system, you need a digital EC meter (often called an EC pen). This device passes a tiny electrical current between two metal electrodes at its tip to measure how easily electricity moves through the nutrient water.
1. Stir Your Reservoir
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Always mix your water thoroughly before testing.
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Nutrients can settle at the bottom, which will give you a false, low reading at the top.
2. Take the Reading
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Remove the protective cap and turn the digital meter on.
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Submerge the tip into the water up to the immersion line (do not drop the entire screen underwater).
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Stir the water gently with the pen to dislodge any air bubbles trapped around the metal sensors.
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Wait 10 to 15 seconds for the digital display numbers to stop shifting.
3. Read the Unit Correctly
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Check the decimal point on your screen.
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Most standard meters read in mS/cm (milliSiemens per centimetre), displaying numbers like 1.2 or 2.0.
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Some meters read in µS/cm (microSiemens per centimetre). If your screen shows a large number like 1200, divide it by 1,000 to get your EC value (1.2).
4. Rinse and Store
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Shake off excess nutrient water, rinse the tip with distilled or tap water, and put the cap back on.
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Unlike pH pens, EC sensors do not need to be kept wet in storage solution.
Reading Your Plant's "Thirst Signals"
Testing your EC daily tells you exactly what your plants are doing. Compare your EC level against your water level over a 48-hour period:
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EC drops, Water level drops: Your plants are healthy and eating nutrients faster than they are drinking water. You need to add more nutrients next time you top up.
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EC rises, Water level drops: Your plants are drinking water but leaving the nutrients behind. The solution is getting too salty and strong. You need to dilute the tank with plain, fresh water immediately to prevent nutrient burn.
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EC stays stable, Water level drops: Perfect equilibrium! Your plants are consuming water and food at the exact same rate.
Adjusting the EC
1. How to Lower Your EC (If it is too high)
When your EC is too high, the water is too salty. Your plants will get nutrient burn because the roots cannot drink.
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The Fix: Add plain, un-nutriated water directly to your reservoir.
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How to do it: Scoop out a few litres of your strong nutrient water if your tank is already full, then top it back up with fresh tap or filtered water. Stir well and re-test until the EC drops back down to your target.
2. How to Raise Your EC (If it is too low)
When your EC is too low, your water is too weak. Your plants are starving and will grow slowly with pale, yellowing leaves.
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The Fix: Add more concentrated liquid (stock) hydroponic nutrients to the reservoir.
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How to do it: Mix your liquid or powder fertilisers into a small jug of water first to dissolve them completely. Pour this strong mix into your main reservoir in small stages, letting it circulate for 5 minutes before re-testing.
Never add raw, un-dissolved powder nutrients straight into your reservoir in a live system, as this can shock and chemically burn your plant roots. Always dilute your adjustments first.