EC + pH cheat sheet
One A4 page to hang next to your reservoir or grow tent. For hydro, coco and soil, for any crop you grow indoors. Free, no email address needed.
Targets at a glance
According to an Ohio State University study (Gillespie, on hydroponic basil), pH 5.5–6.5 is the range typically considered optimal for a hydroponic nutrient solution; outside it, plants tend to show nutrient disorders because nutrients are less available. For coco and soil: follow your nutrient label.
EC per growth stage: an example chart
The EC you aim for depends on your nutrient brand and your medium. Use your own nutrient's chart. As an illustration, the General Hydroponics Flora Series feedchart (“medium feed”) lists:
| Stage (simplified from the feedchart) | EC (mS/cm) |
|---|---|
| First week | 0.5–0.6 |
| Growth | 1.0–2.0 |
| Early and mid bloom (bloom week 1–5) | 1.6–1.9 |
| Late bloom (bloom week 6–7) | 1.0–1.3 |
| Ripen (bloom week 8) | 0.7–0.9 |
Source: General Hydroponics, Flora Series feedchart (read on 4 November 2026). That is one brand's chart, with no pH values and no separate values for soil. Your own nutrient label always comes first.
Calibrating (pH pen)
- Some pH 7 buffer in a clean glass, probe in (as deep as the manual says).
- Start calibration, wait until the reading settles, confirm.
- Rinse with distilled water, pat dry (do not rub).
- Repeat with pH 4 buffer (a 3-point meter also with the third buffer from the manual).
- Check: measure a fresh pH 7 buffer again. If the meter is clearly off, calibrate again or check the manual to see whether the probe needs replacing.
Rhythm: follow your meter's manual. According to Bluelab, the Bluelab pH Pen gives a calibration reminder after 30 days. An EC pen you calibrate yourself is calibrated with a calibration solution, for example 1413 µS/cm (the value Hanna Instruments specifies for the HI98303), as often as the manual says.
Temperature matters
EC depends on the temperature of your solution. Always measure at the same temperature, or use a meter with automatic temperature compensation (ATC).
Storage
Many pH probes must be kept moist, in storage solution if your meter calls for it. Follow your meter's manual.
The 3 most common problems
| What you see | Likely cause | Do this |
|---|---|---|
| pH drops | In a hydro system the pH of your reservoir can drift over time | Measure regularly; correct with pH Up from your nutrient brand: small amounts, stir, wait a moment, measure again. |
| EC stays too low | Too little nutrient, or a two-part (A and B) nutrient not mixed as the label says | First check you dosed to your brand's chart; then raise it in small steps and measure again. |
| EC stays too high | Salt build-up in the medium | Flush with pH-adjusted water without nutrients; measure the runoff EC and only feed again once it has come down. |
Golden rule: pH Up/Down in small steps: add, stir, wait a moment, measure again. Measure what you give and, if you can, what drains from the pot.
Summarised from our pH and EC beginner's guide (Dutch-language article: meters, explanation and background). Desk research by the FutureKweek editorial team, AI-assisted; not tested by us in our own grow. futurekweek.com