pH and EC – Why They're Key and How to Measure Them

pH and EC – Why They Are Key and How to Measure Them

You can have the best lighting, a perfect grow box, and premium fertilizers – but without controlling the pH and EC of your irrigation solution, plants will never reach their true potential. Incorrect pH blocks nutrient uptake (known as nutrient lockout), while inappropriate EC causes either starvation or chemical root burn.

This guide explains what pH and EC mean, what the optimal values are for different growing media, how to correctly measure and adjust parameters, and how to recognize problems before they cause irreversible damage to your crop.

1. What is pH and why does it matter

Definition of pH

pH (potential of Hydrogen) is a logarithmic scale from 0 to 14 that expresses the acidity or alkalinity of a solution. A value of 7.0 is neutral, below 7.0 the solution is acidic, above 7.0 it is alkaline. The logarithmic nature of the scale has a practical impact: a difference of one pH point represents a tenfold change in hydrogen ion concentration. A shift from pH 6.0 to 5.0 is therefore not a small adjustment – it is a fundamental chemical change.

Why pH is critical for plants

Plants absorb nutrients from soil or solution in the form of ions. Each element has a specific pH range in which it is sufficiently soluble and available to roots. Outside this range, nutrients become "locked" – they remain present in the substrate but the plant cannot absorb them. This phenomenon is called nutrient lockout and is one of the most common causes of apparent deficiencies even when fertilizing correctly.

Typical signs of incorrect pH:

• Yellowing of leaves (chlorosis) – most often lack of nitrogen, iron, or magnesium, even though nutrients are present in the solution.
• Brown spots and burned leaf edges – the result of imbalance between elements, where excess of one blocks uptake of another.
• Slowed growth and weak stems – overall limited nutrient uptake manifests as reduced vitality of the entire plant.

2. Optimal pH for different media

Each growing medium requires a different pH range for the irrigation solution. The key is to match the target pH to the specific substrate – what works for soil does not work for hydroponics.

Tip: Do not try to maintain a single fixed pH value. Slight fluctuation within the recommended range (known as pH drift) is intentionally desirable – at different points in the range different nutritional elements are optimally available, so the plant receives more diverse nutrition.

3. Nutrient availability table by pH

The table shows how a specific pH value affects the accessibility of individual macro- and micronutrients to plant roots.

Key takeaways from the table:

• At pH below 5.5, micronutrients (Fe, Mn, Zn, Cu) are readily available, but calcium and magnesium become locked – the plant suffers their deficiency despite fertilizing.
• At pH above 6.5, iron, manganese, and phosphorus begin to become unavailable – typically manifesting as chlorosis on young leaves.
• The range 5.8–6.3 represents the so-called sweet spot where the vast majority of elements are simultaneously readily available.

4. What is EC and why measure it

Definition of EC

EC (Electrical Conductivity) expresses the electrical conductivity of a solution in units of mS/cm (millisiemens per centimeter). Nutrient ions dissolved in water conduct electric current – the higher the nutrient concentration, the higher the measured EC. It is therefore an indirect but reliable indicator of the total mineral load of the solution.

EC does not distinguish which specific nutrients are present – it measures their combined amount. This is why it is important to monitor EC in combination with properly formulated fertilizing, not as a standalone quality indicator.

Relationship between EC and other units

Caution: When reading English-language sources or fertilizer instructions, always verify whether ppm values are stated on a 500 or 700 scale. Both are widely used in practice and confusing them leads to significant overfertilizing or underfertilizing. Most reliable is to work directly with EC in mS/cm and use conversions only when necessary.

5. Optimal EC by growth stage and medium

Important – EC of source water: Always measure the EC of tap or filtered water before adding any fertilizers. If your water has an EC of 0.4 mS/cm and the target solution value is 1.8 mS/cm, you are effectively adding fertilizers for only 1.4 mS/cm. Without this step you risk systematic overfertilizing, which may not manifest immediately but gradually weakens the root system.

6. How to measure pH

Types of pH meters

1. Digital pH meter with electrode – the most accurate method available to growers (accuracy ±0.01–0.05 pH). Measures by direct contact of glass probe with solution. Requires regular calibration, but with proper care lasts several years.
2. pH drops (indicators) – inexpensive and quick approximate method (accuracy ±0.5 pH). Adequate for simple control, but insufficient for precise cultivation management.
3. pH test strips – cheapest option with accuracy ±0.5 pH. Suitable at most for one-time approximate measurement; for regular solution monitoring, their accuracy is too low.

Correct pH measurement procedure

1. Calibrate the pH meter using two calibration solutions – pH 4.0 and pH 7.0 (two-point calibration covers the grower's working range).
2. Rinse the probe with distilled water and gently dry it.
3. Immerse the probe in the solution sample and wait for the value to stabilize (10–30 seconds depending on device model).
4. Record the measured value.
5. After measurement, rinse the probe with distilled water and store it in KCl storage solution – the glass electrode must not dry out.

How to adjust pH

• Lowering pH (solution too alkaline): add pH Down based on phosphoric or citric acid. Always add only small amounts – in concentrated solution a few drops are enough.
• Raising pH (solution too acidic): add pH Up based on potassium hydroxide. Again, drop by drop, stir and remeasure after each addition.

Critical rule: Always adjust pH after adding and mixing all fertilizers. Fertilizers themselves significantly change solution pH and the final value may differ from pure water by more than one point.

7. How to measure EC

Types of EC meters

1. Digital EC meter – two electrodes measure solution conductivity; accuracy typically ±2%. Requires periodic calibration, otherwise values gradually drift.
2. Combined EC/pH meters – one device for both values. Practical and economical, suitable for most hobby and semi-professional growers.
3. Continuous monitors with probe – permanently immersed electrodes with external display or datalogger. Ideal solution for hydroponic systems where continuous monitoring without manual measurement is desired.

Correct EC measurement procedure

1. Calibrate the EC meter using a certified calibration solution (most commonly 1.413 mS/cm or 2.76 mS/cm depending on manufacturer).
2. Check the temperature of the solution – EC is temperature-dependent and at 25 °C results differ from measurements at 18 °C by several percent. Modern meters with ATC function (automatic temperature compensation) automatically correct this difference.
3. Immerse the probe in the solution and wait for the value to stabilize.
4. Record the result.

You will find a selection of pH meters, EC meters, and combined devices on Pestík.cz. Do not forget calibration solutions – without regular calibration, measured values are unreliable regardless of instrument price.

8. Calibration – how often and why

Electrochemical probes naturally change with age and solution contamination – a drift of 0.2–0.3 pH per month is not uncommon even in quality instruments. Regular calibration is therefore necessary, not optional.

Calibrate pH and EC meters:

• Before first use – always, even with a new device straight from the box.
• At least once every two weeks with regular daily measurement.
• After a longer break – if the device has not been used for more than a month.
• Whenever error is suspected – if measured values do not match the visual state of plants or change rapidly and unexpectedly.

Tips for longer meter lifespan

• Never let the pH meter probe dry out – the electrode will lose function and calibration. Store it immersed in KCl solution.
• Rinse the EC probe with distilled water after each measurement to prevent salt buildup.
• Do not expose meters to extreme temperatures or direct sunlight.
• Do not reuse calibration solutions after probe contact – the probe will transfer ions into them and the solution will lose accuracy. Always pour into a separate container and discard excess.

9. Most common pH and EC measurement errors

10. Practical procedure – irrigation step by step

1. Prepare water – ideally reverse osmosis water (EC close to 0.0) or quality filtered water with EC below 0.4 mS/cm.
2. Add fertilizers – follow the dosing schedule of the manufacturer; with multi-component systems, follow the recommended addition order.
3. Mix thoroughly – ensure all fertilizer components dissolve evenly.
4. Measure EC – compare with target value for current growth stage (see table above).
5. Adjust EC – add pure water to lower, or fertilizer dose to raise.
6. Measure pH – compare with recommended range for your medium.
7. Adjust pH – add pH Down or pH Up drop by drop, always with control remeasurement after mixing.
8. Irrigate and measure runoff – after irrigation, collect a sample of drainage solution and measure its pH and EC. This "runoff test" reveals what is actually happening in the root zone.

Runoff test in practice: If runoff EC is significantly higher than irrigation solution EC (difference over 0.5 mS/cm), salt buildup is occurring in the substrate. Flush the substrate with 2–3 times its volume of clean water with adjusted pH, then return to normal fertilizing. If runoff pH is outside the range by more than 0.5 points, chemical processes are occurring in the substrate (organic matter decomposition, mineral precipitation) that need to be addressed by flushing and possibly reviewing the substrate used.

Frequently Asked Questions (FAQ)

How often should I measure pH and EC?

Frequency depends on the growing medium. In hydroponics, measure daily – systems without substrate have no buffering capacity and parameters can change quickly. In coco substrate, 2–3 times per week is sufficient. In soil, 1–2 times per week is enough because soil microbiota and organic matter naturally stabilize pH and changes occur more slowly.

What should I do if runoff pH is significantly different from irrigation solution pH?

A deviation greater than 0.5 points indicates chemical changes inside the substrate – most often salt buildup or organic matter decomposition. Flush the substrate with 2–3 times its volume of water with adjusted pH (no fertilizers), allow it to drain completely, then return to normal irrigation. If the problem recurs, consider replacing part of the substrate or switching to a different medium.

Can I use vinegar to lower pH?

Not recommended. Vinegar (acetic acid) is chemically unstable in aqueous solution – pH will return to the original value after a while and the solution requires repeated adjustments. Furthermore, in excess it disrupts the microbial balance in the substrate. Use products designed for this purpose, pH Down based on phosphoric acid, which are stable, do not interfere with nutrient solution composition, and are safe for plants.

Do I need reverse osmosis?

If your tap water has EC above 0.5 mS/cm or contains higher amounts of chlorine, chloramines, or calcium, investment in RO filtration is worthwhile – especially in hydroponics where hard water complicates precise EC and pH management. In soil, harder water can be managed more easily, but even there lower source water EC gives the grower greater control over plant nutrition.

What is the difference between cheap and expensive pH meters?

Main differences lie in accuracy (±0.1 pH in basic models vs. ±0.01 pH in professional ones), speed of value stabilization, quality of glass electrode and its lifespan. For hobby growing, a mid-range meter with ±0.05 pH accuracy is fully sufficient. The deciding factor, however, is not instrument price but regular calibration – a correctly calibrated cheap meter is always more accurate than an expensive uncalibrated one.

Sources

• pH, EC and Temperature – Bluelab
• Electrical Conductivity and pH Guide for Hydroponics – Oklahoma State University
• How pH affects Cannabis Plants (Chart) – Dutch Passion
• Complete EC & pH Levels Chart – Aqua Gardening
• Nutrient Lockout: What It Is and How To Prevent It – Advanced Nutrients
• pH and EC Levels by Growth Stage – Green Genius