EC is a measurement of the levels of salts in your hydroponic system. It helps you determine the nutrient concentration in the nutrient solution.

Monitoring the EC level is critical to the health of a hydroponics garden. Depending on the nutrient strength of the water, you may be overfeeding or underfeeding your plants.

So, what should the EC be for hydroponics? Keep reading to find out.

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What Is EC?

Electrical conductivity (EC) is a measurement of the potential for a material, such as water, to conduct electricity. This is also called “molar conductivity.”

What Is EC?

The ability of water to carry electrical currents depends on the presence of mineral ions. Ions transport electronics through the water molecules. 

When you add a nutrient mix to the water solution, the plant food dissolves in the water. Dissolved solids dissociate into ions in the water, which increases the concentration of soluble minerals and vitamins.

Water with heavy mineral content has increased molar conductivity. Demineralized water, reverse osmosis water, and pure rainwater offer low conductivity, as they contain fewer minerals.

Basically, the EC level increases as you add nutrients. A low EC measurement indicates that the water solution lacks nutrients.

EC is expressed using a variety of different units of measurement. However, the most common unit is siemens per square meter (S/m2) and milli-siemens per centimeter (mS/cm).

Quick Pro Tip: Start with distilled water instead of tap water. EC levels indicate the concentration of mineral salts in the water, but not all salts offer nutritional value.

Faucet water often contains heavy metals, chloride, and sodium, which offer no nutritional value. High levels of certain minerals may also limit nutrient uptake of essential minerals.

EC Versus Parts Per Million (PPM)

Parts per million (ppm) is another unit of measurement used by hydroponic farmers. It’s the most common method for measuring total dissolved solids (TDS), especially in North America.

As with the EC level, the ppm level indicates the electrical conductivity of the water. In fact, it’s calculated using the EC value. 

As PPM is determined using calculations, it offers less accuracy compared to EC readings.

The companies that produce ppm meters can also choose from three separate conversion factors. A TDS meter from one manufacturer may offer different results compared to a meter from another company.

How Do PH Levels Impact EC Values?

Along with EC and ppm, hydroponic growers often measure pH levels. The pH level measures the acidity of the water. 

pH is measured on a scale from 0 to 14 using a pH meter. Zero to 7 is acidic and 7 to 14 is basic or alkaline. Most plants prefer a slightly acidic pH reading, with an average pH of 5.4 to 6.0. 

A high pH can lead to a nutrient deficiency. If the water has a pH level, the alkalinity of the growing media increases, which makes the micronutrients less soluble.

You can have a high EC measurement and still deprive your plants of essential nutrients, such as iron. Plants with an iron deficiency tend to exhibit stunted growth and may develop chlorosis (yellowing of the leaves).

Using a high ammonium fertilizer instead of a high nitrate fertilizer can help reduce pH levels. Adding iron sulfate also helps reduce the alkalinity of the water and growing medium.

A low pH is less common but can still stunt growth. Adding small amounts of sodium bicarbonate can increase the pH levels.

How Do You Test for EC in Hydroponics?

An EC meter is typically used to measure EC levels. The meters either include an LCD screen or LED indicators to display the EC reading. 

Many meters also provide EC and PPM readings, allowing you to easily use whichever unit of measurement you prefer. 

Always clean the probe of the meter with fresh water and a dry cloth before taking a reading. You typically need to hold the meter in place for one to two minutes to take an accurate reading. Holding the meter in the water allows it to reach the same temperature.

What Is the Ideal EC Level in Hydroponics?

The nutrient water should have an EC reading between 1.2 and 2.5 S/m2, depending on its growth stage. The ideal range for plants during the vegetative stage is 1.2 to 1.6 S/m2. Once plants start watering, the EC level should be between 1.6 and 2.5 S/m2. 

Different plant species also have different nutrient requirements. Here are the preferred nutrient concentrations for some of the most common plants:

  • Lettuce – 1.2 to 1.8
  • Herbs – 1.0 to 1.6
  • Asparagus – 1.4 to 1.8
  • Strawberry – 1.8 to 2.2
  • Spinach – 1.8 to 2.3
  • Tomatoes – 2.0 to 4.0

Due to the various nutrient requirements, it’s often best to grow certain types of plants separately. For example, tomatoes need a higher nutrient strength compared to lettuce, which could create a problem.

What Happens If EC Is Too Low?

Lower EC levels indicate that your nutrient solution doesn’t contain enough nutrients. You need to add more fertilizer. Adding one milligram of nutrients per litre of water increases the EC level by about 0.002.

For example, if you need to increase the EC level by 1, you need about 500 milligrams of nutrients (1 divided by 0.002 = 500).

What Happens If EC Is Too High?

A high EC level indicates that you’re probably adding too much plant food. However, high mineral levels could also be due to mineral-heavy water, unhealthy plants, or a high pH value.

Using water from your faucet may add excess minerals, as water from the faucet often contains heavy metals. Flush a portion of the tank and replace it with distilled water. Check the EC levels again and add plant fertilizer if needed. 

High pH levels and an unhealthy plant root zone leads to nutrient lockout, which leaves more minerals in the water. Consider pulling unhealthy plants and correcting pH levels before lowering EC levels. 

Summary

Checking the electrical conductivity (EC) allows you to monitor the nutrient levels in your hydroponic solution. The minerals that you add increase the conductivity of the water.

If the EC levels are low, your solution needs more nutrients. Add more mineral salts until you reach the desired EC reading. 

If the EC levels are high, you’re likely overfeeding your plants. Dilute the nutrient solution by adding fresh water. You may also cleanse the water with a reverse osmosis machine or a carbon filter, but these options involve more work.