pH and EC for Growing Cannabis — A Beginner's Guide

By the FutureKweek editorial team · FutureKweek · 2026-06-04

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pH and EC are the two numbers that separate a good harvest from a failed one. A grower with no pH meter is just hoping. This guide: which meter to buy, how to calibrate it, and the values to hold per growth stage — with the fix for the three most common readings that go wrong.

Before you buy — watch this

What are EC and pH, really?

pH (potentia hydrogenii) measures acidity on a logarithmic 0–14 scale. 7.0 is neutral (pure water), <7 is acidic, >7 is alkaline. For growing, pH decides whether nutrients are available to the roots. 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.

EC (electrical conductivity) measures the amount of dissolved salts/nutrients in solution, in mS/cm (milliSiemens per centimeter). Higher EC = more nutrients. EC tells you how much you've fed, but not what. It's a total reading — no replacement for a nutrient schedule, but the check that you're not over- or under-dosing. (US growers will also see TDS/ppm; how ppm relates to EC depends on the scale your meter uses.)

Which meters to buy?

Two instruments: one for pH and one for EC.

pH meter — best choices

A generic budget pH pen looks attractive. Check whether you can calibrate it and whether the probe can be replaced: a meter you cannot calibrate, you cannot check. Bluelab pH Pen on Amazon.

EC meter — best choices

If you're just starting and the Bluelab Truncheon price is too much, a cheaper Hanna or Apera EC pen is a workable start. Calibrate it with a calibration solution, for example 1413 µS/cm (the value Hanna Instruments specifies for the HI98303), as often as the manual says. Apera EC20 EC pen on Amazon.

Calibrating — the steps nobody explains

What you need

• pH 4 buffer solution
• pH 7 buffer solution
• A third buffer — only if your meter does a 3-point calibration (see its manual; the Bluelab pH Pen uses 2-point calibration, per Bluelab)
• Distilled water (to rinse between buffers)
• Probe storage solution — if your meter calls for it

A pH 4 + 7 buffer kit on Amazon.

pH calibration procedure (Bluelab pH Pen)

1. Pour some pH 7 buffer into a clean cup and put the probe in, as deep as the manual says.
2. Start calibration and wait until the reading is stable, then confirm.
3. Rinse the probe with distilled water. Dab dry with a tissue (don't rub).
4. Repeat with pH 4 buffer. For the Bluelab pH Pen, that completes the 2-point calibration.
5. A 3-point meter: also repeat with the third buffer from its manual.
6. Store the probe as the manual says.

EC calibration procedure

Bluelab Truncheon: according to the maker it needs no calibration (it comes factory-calibrated). Hanna and generic EC pens: calibrate with a calibration solution (Hanna specifies 1413 µS/cm for the HI98303), as often as the manual says.

Target values by growth stage

The EC you aim for depends on your nutrient brand and your medium; use your own nutrient's chart. As an example, the General Hydroponics Flora Series feedchart (“medium feed”, read on 4 November 2026) lists:

That is one brand's chart, with no pH values. For pH in hydro, see the Ohio State study cited above; in coco, follow your nutrient label.

Still choosing a hydro system? Hydroponics for beginners compares them.

Soil

For pH in soil, follow the label of your soil and nutrient. The feedchart above gives no separate soil values; with pre-amended soil (for example Biobizz All-Mix) follow the label of your soil and nutrient.

The 3 most common readings that go wrong — and how to fix them

Problem 1: pH drops

Symptoms: Leaf tips turn brown. Yellowing between veins. Roots turn grey.

Cause: In a hydro system the pH of your reservoir can drift over time.

Fix: Measure regularly and correct with pH-Up from your nutrient brand: small amounts, stir, wait a moment and measure again.

Problem 2: EC stays too low despite feeding

Symptoms: Leaves light yellow. Slow growth. With coco: substrate feels heavy (too much water).

Cause: Two options. (1) You added too little nutrient. (2) An A+B nutrient is mis-dosed — usually too little "A" (the calcium-magnesium component).

Fix: First check that you dosed to your brand's chart. With a two-part (A and B) nutrient the ratio is on the label; follow it. Then raise the dose in small steps and measure again.

Problem 3: EC stays too high after flushing

Symptoms: Leaf tips burn (brown on the tips). Slow uptake of fresh water.

Cause: Salt build-up in the substrate.

Fix: Flush with pH-adjusted water and no nutrients. Measure the runoff EC (the water draining from the pot) and only start feeding again once it has come down.

Common beginner mistakes

• Forgetting probe storage: many pH probes must be kept moist, in storage solution if your meter calls for it. Follow your meter's manual.
• Too much pH-Up or pH-Down at once: pH adjuster is concentrated. Add a small amount, stir, wait a moment and re-measure before adding more.
• Measuring EC without temperature correction: EC depends on the temperature of your solution. Measure at the same temperature, or use a meter with automatic temperature compensation (ATC).
• Cuttings on a full feed schedule: cuttings have no roots yet, so they take up little. Start low and follow your nutrient brand's chart for the first week.