An Introduction to pH and EC

pH & EC

An Introduction to pH and EC

When growing in soil, all microbes (as well as the soil itself) help to make nutrients available to the plant. However when removing the soil by growing hydroponically, the responsibility falls onto the grower. This can prove tricky, but when mastered can be extremely rewarding. Because by understanding how to measure pH and EC, you’ll be able to precisely monitor and control nutrient and salt levels throughout the different plant growth stages.

What is pH?

To explain pH, we’ll first go into the maths. pH is a measure of how acidic or alkaline a solution is, controlled by the activity of hydrogen cations (H). More specifically, pH is the decimal logarithm of the reciprocal of hydrogen ion activity. This sounds more complicated than it is. By understanding this equation, a bit more, we realise why controlling the pH in your hydroponic system is so important.

pH = log10 (1/αH+)

(αH+ is the activity of the Hydrogen cation)

Let’s break things down into simple stages. First thing is the log10 part of the equation. This means that each time you go up or down by one whole pH point (e.g., 5 → 4) the change in the acidity (the hydrogen activity) is changing by a factor of 10. pH 4 is ten times more acidic than pH 5, and a hundred times more acidic than pH 6. This explains why precise control down to 0.1 on the pH scale is necessary.

The second part of the pH is the 1/αH+ bit. Basically, this means that pH is the inverse of the hydrogen activity. So as the activity of the hydrogen increases, the pH decreases. This is why all acids have hydrogen in them which they release into the solution to increase activity and lower pH (e.g., HCl = hydrochloric acid).

The pH scale runs from 0 – 14, with 0 being very acidic and 14 being very alkaline. When growing you won’t see those extremes, with usual values between 5 and 7, ideally between 5.8 and 6.2.

Why is pH important to plants?

The pH of the soil, or hydroponic solution, controls the availability of the nutrients to the plant. The elements themselves are still there, what changes is the form they are in. Plants need nutrients to be in a water-soluble form. This is so they can take them into their ‘bloodstream’ (the sap) and transported to the required area. A change in the pH can change the form and therefore reduce or increase the availability of nutrients. What makes things complicated is that different nutrients are available at different pH ranges. In hydroponics the ideal pH range is between 5.8 and 6.2, with soil the target being slightly higher, nearing 6.5. This range provides the plant with the maximum availability to the most nutrients. pH testing kits and pens provide growers with a very useful tool to help maintain healthy plant growth.






What is EC?

EC stands for electrical conductivity. It’s a measure of how well a material (in the case of hydroponics, a solution) conducts electricity. This is a function of the number of electrolytes (charge carrying particles) in the solution. The more electrolytes, the higher the conductivity. The higher the charge carried by each particle, the higher the conductivity. There are other factors as well involving particle shape, temperature, solvent type etc. But for our purposes, EC is a good measure of how much salt is in your hydroponic reservoir.

While it will give you basic information, EC will not tell you what salts are in your solution. This is why some growers use water that has been filtered by reverse osmosis. This is to remove everything (even things smaller than salts such as bacteria and viruses) so they can start from a blank slate. Growers then know exactly what’s in their water, and can use nutrient to tailor their grow.

Why measure EC?

Nutrients use salts to provide plants with all the elements they need, from Boron (B+) to Zinc (Zn2+). High salt levels can hinder plant growth without showing other obvious symptoms. At extremes, high salt can cause discoloration and dryness as they impede the plants’ uptake of water. EC monitoring provides a clear way of detecting and regulating salinity levels within your hydroponic reservoir.

In a soil based medium, the amount of salt is controlled by the humate levels (and their cation exchange capacity), the amount of water present (and it’s contact with the roots) and the amount and type of microbes, as well as a whole host of other mechanisms. All these things provide more control. Reducing (but not removing) the chance of over fertilisation when compared with hydroponics. As such, monitoring EC doesn’t play the same role when feeding plants in soil, so following manufacturer guidelines is recommendable.

In Conclusion

At Plant Magic we analysed water samples from around the UK to understand how to make nutrients that balance with the water supply countrywide. Our nutrients are suitable for both hard and soft water variants, helping you to better balance your pH and EC. Where extreme soft water is causing deficiencies, we have Magne-Cal+, a magnesium-calcium supplement that can be used with any growing medium and any nutrient range to help keep plants healthy.