What is EC in Hydroponics? A Detailed Guide 

In hydroponics, “EC” refers to Electrical Conductivity which is a measure of the degree to which a nutrient solution can conduct electricity. Because dissolved salts and minerals conduct this electricity, checking the EC provides growers with an idea about the amount or concentration of nutrients within the water. Keeping the EC in the right range will provide the plants with just the right balance of nutrients for healthy growth. 

EC is merely a reading of how easily an electrical current can pass through a water solution. With a high concentration of dissolved nutrients such as nitrates, EC will go higher. I failed to take EC reading in a new hydroponic system a few years ago, thinking I’d gotten the right amount of nutrients. Obviously, they were wrong, and my lettuce ended up burning. So, let me teach you how to do it correctly.  

The Importance of EC in Hydroponics 

Hydroponically grown plants are highly dependent on the nutrient solution. If EC is too low, the plants will be starved; meanwhile, EC being too high will carry a risk of making them burn. I had one student whose tomato leaves were curling under, and I asked them about the details. I learned that the EC level was too high, which meant evaporation concentrated the salt in the solution. With regular checks, now I can tell how much fertilizer is in water. So, finding the right EC level is highly important.  

How to Measure EC? 

The most commonly used measurement tool for EC is the EC meter. It sends a small current to the solution, which makes it possible to read how much electricity the solution can generate. I used a pen meter, which was cheaper but, unfortunately, was a waste of time. The right criteria for measuring meters you should follow are the following: 

Types of Meters to Measure EC 

The standard units of measure for EC are in mS/cm (milliSiemens per centimeter) or µS/cm (microSiemens per centimeter); this reading provides a direct relation to the solution’s nutrient concentration. 

TDS (overall number of substances present in the water), usually expressed in PPM (parts of a substance in one million parts of water), is calculated from the EC readings but is expressed as an estimate of the quantity of dissolved solids in solution. The conversion between the two does vary depending on the meter or standard used, and common conversion factors are 500 or 700; thus, 1 EC may equal 500 PPM or 700 PPM.  

CF (conductivity factor) is another measure of nutrient strength, mainly used in some parts of the world, such as parts of Europe, where 1 CF is generally equal to 10 µS/cm. 

Calibration  

Calibration means the process by which your EC meter or TDS/CF meter is maintained accurately over time. This is because sensor probes tend to either drift or become coated with mineral deposits. 

This can be accomplished simply by first rinsing the probe with distilled or deionized water and then placing it in a calibration solution of an already known value of EC, usually 1.413 mS/cm or 2.76 mS/cm. After the reading stabilizes, the meter would have to be adjusted accordingly either by an auto-adjust, or a small screw, or a digital interface. Finally, re-rinse and test the probe again to confirm its accuracy. Performing this calibration every couple of weeks, or as recommended by the meter’s guidelines, ensures reliable nutrient measurements in your hydroponic system. 

Measurement Frequency  

You should test daily or three days apart, depending on the crop you grow. For instance, I learned not to miss a whole lot of days sequentially or I will have enormous nutrient imbalances. 

EC Guidelines for Different Plants  

Each plant needs a different level of EC measurement. It is important to know them and use them properly based on your choice of plant.  

• Leafy greens like spinach and lettuce: Prefer a milder EC level, roughly 0.8–1.2 mS/cm. 
• Fruiting vegetables, including cucumbers and tomatoes: Around 2.0–2.5 mS/cm. I personally keep them at less than 2.2 when it’s a smaller variety. 
• Herbs such as mint, basil, and peppers: Around 1.8–2.2 mS/cm is ideal. 

During early development, I always used a lower EC level. If you try to boost the EC too soon, you can burn out those delicate roots. I burned an entire tray of basil seedlings overnight when I used nutrition a little too fast.  

Adjusting EC Levels 

When adjusting EC, to increase it, add concentrated nutrition solution or fertilizer. I do it gradually, generally, because I have previously added a lot of fertilizer at once, and my peppers haven’t appreciated the shock. 

To decrease it, add non-fertilized water to dilute the solution. I use reverse osmosis (RO) water, but if your tap water is fairly decent, that will suffice too. Just make slow drops and don’t make large EC drops, for large drops in EC can cause issues too. 

Common Problems and Solutions in EC Usage 

EC usage can be problematic when you are a beginner. Here are some common problems you may face: 

Sudden EC Spikes 

This could be the case with sudden spikes in EC if the nutrient salts may cause a buildup or water evaporates more rapidly than its replacement, hence concentrating the solution. These sudden changes, which may stress your plants, can be avoided by regular checks and adjustments of the system. I normally top off with fresh water in such cases. 

EC Drops  

This can indicate that the plants are hungry or something is wrong with the meter. There was a time when my meter’s battery was low, and it was reading it wrong.  

Salt Build-Up  

Salt will build up over time and stay in the pot or on the roots. I fixed this issue by flushing it with fresh water. Not cleaning these build-ups can be damaging to your plants. 

Temperature Effects  

Warm temperatures cause the EC to rise quickly, especially in small places. Closely monitor the temperature in a greenhouse environment. In winter, the plants use less nutrients, and I sometimes let the EC fall a little below target. Using Automatic Temperature Compensation (ATC) can be helpful. 

Quality Water and Treatment Methods 

If your tap water is high in naturally dissolved minerals, your initial EC can start at 0.5 or even larger. Then add your desired amount of nutrients afterward. That can make it difficult to control your final EC. I run an RO filter in my system because my tap water is fairly harsh. I experienced fewer lockouts when I based my EC on zero or almost zero. 

My EC Experiment 

A while back, I was testing a “floating raft” system for growing lettuce. I started with a 1.0 mS/cm nutrient solution. I checked EC two days at a time, and it increased to 1.3 or 1.4 towards the end of it, most likely through water loss. I simply top off with regular water to 1.1 or 1.2. After three weeks, the heads of the lettuce were big, healthy, and green with no tip burn in sight. I messed up one time when I did not check the reservoir for five days in a row, and EC increased to almost 1.8, and I saw leaf burn. 

FAQs

Can tap water affect the EC reading?  

Yes, tap water can contain dissolved minerals and salts that contribute to the EC reading. It is better to measure the EC of your water source before mixing nutrients. 

Do different plants require different EC levels?

Absolutely yes. Different plants have different nutrient requirements, and so their desired EC levels will change. Research specific plants to find the optimal EC for each type you are growing.