pH and EC: Meters, Test Kits and pH Up/Down
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 or test kit to choose, how to use pH Up and Down, and how to keep a meter 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 and its leaves yellow 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:
| Growing in | Athena | House & Garden |
|---|---|---|
| Coco | 5.8-6.2 | 5.8-6.3 |
| Rockwool | 5.8-6.2 | – |
| Peat-based mixes | 6.0-6.4 | – |
| Soil | – | 5.8-6.3 |
| Hydro (recirculating) | – | 5.7-5.9 |
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?
| Meter | Measures | Good to know |
|---|---|---|
| Bluelab pH Pen | pH | One-button pen for soil, coco and hydro |
| Bluelab Truncheon | EC, CF, TDS | Waterproof and temperature compensated; can't be calibrated, so check it in conductivity standard and clean it at least once a month or it under-reads |
| Aqua Master P50 Pro | pH, temperature | Automatic temperature compensation; replacement probes sold separately |
| Aqua Master E50 Pro | EC, temperature | Backlit display |
| Aqua Master P110 Pro | pH, EC, temperature | All three in one pen |
| GroLine pH/EC Monitor | pH, EC, temperature | Sits in the tank and reads continuously |
| NutSystems pH Test Kits | pH | Colour test, wide or narrow range: an economical way to start |
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.
Testing pH with a colour kit
The NutSystems kit has 20 ml of reagent, a small test tube and a colour chart. Its page sets out the method:
- Put a sample of your feed in the test tube.
- Add a few drops of the pH indicator.
- Compare the colour with the chart to read the pH.
It comes as Wide Spectrum or Narrow Spectrum. The wider range, 4.0-10.0, covers all the makers' targets above (5.7 to 6.4); the page does not give the narrow range in full, so ask us before choosing it. Read the colour in daylight, not under a coloured grow light.
How to measure and adjust a feed
- Mix the whole feed first: water, base nutrients, then each additive, stirring between each. Measure with a measuring jug (up to 2 litres), syringe (10-100 ml) or pipette (3 or 5 ml), not by eye.
- Check the EC. Too high, add water; too low, add a little more base feed. Stir and measure again.
- Check the pH last, once everything is in. Adjust with Growth Technology pH Down or Growth Technology pH Up a few drops at a time, stirring and re-checking each time - it is easy to overshoot.
- In a recirculating tank, check again every day or two: the plants drink water faster than they take up feed, so both readings drift.
pH Up and pH Down
pH Down is an acid and pH Up an alkali, and both can be corrosive neat: follow the label and never mix one with the other. These are the adjusters we sell:
| Product | Does | From the product page |
|---|---|---|
| Growth Technology pH Down | Lowers pH | 250 ml, 1 L and 5 L |
| Growth Technology pH Up | Raises pH | 250 ml and 1 L |
| Intense Pro Series pH Down Ultra | Lowers pH | High strength; add a little at a time, stir and test. Corrosive acid: use protective equipment |
| Intense Down N Dirty | Lowers pH | Methanesulfonic and citric acid. The ml-per-litre dose on its page is against mineral deposits, not for pH |
| Liquid Silicon | Raises pH | An alternative to pH Up with a nutrient that has no silica; follow its label for when to add it |
| Athena Balance | Raises pH | Goes into the water first, before the feed: 0.25-1 ml per litre. Not for Netaflex or other electronic dosers |
| Athena Pro Balance | Raises pH | pH stabiliser; for Netaflex, our Athena feed chart says |
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.
How do I test pH without a meter?
With a colour test kit: a sample in the test tube, a few drops of indicator, then match the colour to the chart. It is less exact than a meter and reads pH only; EC needs a meter.
How much pH Down do I add?
There is no fixed amount: it depends on your water, your feed and how strong your pH Down is. Add a little at a time, stir and re-test. Note what a full tank took as a guide for next time.
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.