pH and EC: Meters, Test Kits and pH Up/Down
Most feed charts give you a pH or 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, so take it from the chart for the feed you use. This is each chart's range, from its weakest feed to its strongest:
| Feed chart | EC (mS/cm) | pH |
|---|---|---|
| Canna Coco | 1.8-2.9 | – |
| Canna Aqua | 1.4-2.7 | – |
| Canna Terra | 1.2-2.5 | – |
| Athena | Blended 1.5-2.6; Pro 2.0-3.0 | 5.8-6.2 coco, rockwool; 6.0-6.4 peat |
| Plant Magic | 0.8-2.2 | – |
| House & Garden | – | 5.7-5.9 hydro; 5.8-6.3 coco, soil |
| Dutchpro | 1.8-2.4 (soil, hard water: 1.8-2.3) | 5.8-6.5 soil; 5.8-6.2 hydro, coco |
The Biobizz, Advanced Nutrients and Hesi charts give doses only, with no EC or pH to aim for.
EC, CF and ppm
CF is EC x 10. Parts per million (ppm or TDS) is usually EC x 500 or x 700, depending on the scale the meter uses:
| EC (mS/cm) | CF | ppm, 500 scale | ppm, 700 scale |
|---|---|---|---|
| 0.4 | 4 | 200 | 280 |
| 0.8 | 8 | 400 | 560 |
| 1.2 | 12 | 600 | 840 |
| 1.6 | 16 | 800 | 1,120 |
| 2.0 | 20 | 1,000 | 1,400 |
| 2.4 | 24 | 1,200 | 1,680 |
| 2.8 | 28 | 1,400 | 1,960 |
| 3.0 | 30 | 1,500 | 2,100 |
The Bluelab Truncheon measures all three: EC, CF and TDS. If a chart gives ppm, check which scale it and your meter use 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 6.5); 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.
- 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 and probe care
Calibrate weekly, as Growth Technology advise, and any time a reading looks wrong. Calibrate a pH meter in buffer (pH Pen Calibration Fluid or Hanna Calibration/Buffer Solutions) and an EC meter in conductivity standard (EC Pen Calibration Fluid or Hanna's). A Bluelab Truncheon can't be calibrated, only checked in the standard. Between uses keep a pH probe wet in pH Probe Storage Solution and clean it regularly with pH Probe Cleaning Solution; our guide on how to calibrate a pH pen has the steps.
Quick answers
Do I check pH or EC first?
Mix everything, check the EC, then check and adjust the pH last.
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. If it still won't calibrate after a clean, the probe is probably worn out.
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
- How to calibrate a pH pen
- 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.