pH and EC Meters: How to Measure, Calibrate and Look After Them

Every feed chart gives you a pH and an EC to aim for, and the only way to hit them is to measure. This guide covers what pH and EC actually tell you, the targets the nutrient makers publish, which meter to choose, and how to keep it reading true.

What pH and EC tell you

• pH is how acidic or alkaline the water is. It matters because it decides which nutrients the roots can take up: a feed with everything in it can still leave a plant short if the pH is off.
• EC (electrical conductivity) is how much dissolved feed is in the water. More nutrient in the tank means a higher EC, so it tells you how strong the feed is. It's measured in mS/cm.

pH targets from the nutrient makers

There is no single right pH: it depends on what you grow in. These are the ranges the makers print on their own charts:

Starter plugs can be different again: Jiffy-7 peat pellets have a pH of 5.3, so you don't need to adjust tap water for them.

EC targets: use your feed chart

The right EC changes week by week and from one feed to another, so take it from the chart for the feed you use. Ours set out the makers' own figures: Canna Coco, Canna Terra, Canna Aqua, Athena, Plant Magic. The Biobizz and Advanced Nutrients charts give doses rather than EC targets.

EC, CF and ppm

Meters show strength in different units. CF is EC multiplied by ten, so EC 1.5 is CF 15. Parts per million (ppm or TDS) depends on the scale the meter uses: on Athena's chart an EC of 2.0 is 1,000 ppm on the 500 scale and 1,400 ppm on the 700 scale. If a chart gives ppm, check which scale before you compare.

Which meter?

If you only buy one thing, make it a pH meter: an EC reading tells you the feed is strong enough, but a wrong pH can lock the plant out of what's there. All our meters are in Nutrient Management.

How to measure and adjust a feed

1. Mix the whole feed first: water, base nutrients, then each additive, stirring between each. Measure with a measuring jug, syringe or pipette, not by eye.
2. Check the EC. Too high, add water; too low, add a little more base feed. Stir and measure again.
3. Check the pH last, once everything is in. Adjust with pH Down or pH Up a few drops at a time, stirring and re-checking each time - it is easy to overshoot.
4. In a recirculating tank, check again every day or two: the plants drink water faster than they take up feed, so both readings drift.

Calibrating

Growth Technology, who make our calibration fluids, say all measuring equipment should be calibrated weekly to keep nutrient readings accurate. A meter that has drifted gives a wrong answer for every feed you mix.

• pH meters are calibrated in buffer solution: pH 4 and pH 7 buffers or Hanna pH 4.01 and 7.01 and Quick Cal. Follow your meter's instructions for which buffers and in what order.
• EC meters are checked or calibrated in conductivity standard: 1.41 or 2.76 mS/cm, or Hanna's 1.413 and 5 mS/cm.

Looking after a pH probe

• Keep the probe wet. Probe storage solution keeps the sensor hydrated between uses; a dried-out probe reads badly and wears out sooner.
• Clean it regularly. Probe cleaning solution lifts the salts, minerals and residue that build up and throw readings off. Groline also make cleaning and storage solutions.
• If a meter still won't calibrate after a clean, the probe is probably worn out. Some meters, like the Aqua Master P50 Pro, take a replacement probe.

Quick answers

Do I check pH or EC first?

Mix everything, check the EC, then check and adjust the pH last.

How often should I calibrate?

Weekly, as Growth Technology advise, and any time a reading looks wrong.

Why does my pH pen keep drifting?

Usually a dirty or dried-out probe, or one that hasn't been calibrated for a while. Clean it, calibrate it, and store it in storage solution.

More Growers' Guides

• Canna Coco feed chart
• Athena feed chart
• Hydroponics: the systems explained
• Autopot systems explained

Not sure what you need? Call the shop on 0117 971 3000 or pop in to the Bristol store and we'll help you pick.