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

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

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. At pH 5.5–6.5 most are available; outside that you "lock out" nutrients — they sit in solution but the plant can't take them up.

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; ~1.0 mS/cm ≈ 500 ppm on the 500-scale.)

Which meters to buy?

Two instruments, not one combo. Combined meters (the $100–300 range) compromise on both. Separate pens are more accurate and last longer.

pH meter — best choices

The generic $15 pH pen looks attractive, but the trade-offs are in the table above: not waterproof, and no probe replacement — so once the probe drifts, the whole pen is consumable. One mis-measured calibration costs you a whole cycle of yield — don't save money on your pH meter. Bluelab and Apera pens on Amazon.

EC meter — best choices

If you're just starting and the Bluelab Truncheon price is too much, a $40 Hanna or Apera EC pen is a workable start. Calibrate monthly with 1413 µS/cm buffer solution. EC/TDS meters on Amazon.

Calibrating — the steps nobody explains

What you need

• pH 4.00 buffer solution (50–250 mL bottle)
• pH 7.00 buffer solution (50–250 mL bottle)
• pH 10.01 buffer solution — only for 3-point calibration (the Apera PH60 does this; the Bluelab pH Pen doesn't need it)
• Distilled water (to rinse between buffers)
• Probe storage solution (KCl) — for storage between sessions, lasts 12+ months

A pH 4 + 7 buffer kit on Amazon is a few dollars and lasts a long time.

pH calibration procedure (Bluelab pH Pen)

1. Pour 30–50 mL of pH 7 buffer into a clean cup. Submerge the probe 2–3 cm.
2. Press the cal button. Wait 30–60 seconds until the reading is stable. Press again to confirm.
3. Rinse the probe with distilled water. Dab dry with a tissue (don't rub — it damages the glass bulb).
4. Repeat with pH 4 buffer. For the Bluelab pH Pen, that completes the 2-point calibration.
5. For the Apera PH60: also repeat with pH 10.01 (3-point calibration).
6. Store the probe in KCl solution.

EC calibration procedure

Bluelab Truncheon: never calibrate — the factory does it for 5 years. Hanna and generic EC pens: calibrate monthly with a 1413 µS/cm buffer (the hydroponics standard).

Target values by growth stage

Hydro & Coco (5.8–6.2 pH range)

Soil (6.2–6.8 pH range)

Soil has higher pH buffering from organic matter. Target pH is 6.2–6.8. EC values are 20–30% lower than hydro because the soil itself supplies nutrients (especially with Biobizz All-Mix-style pre-amended soil).

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

Problem 1: pH drops to 5.0–5.5

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

Cause: In hydro the roots are active — they release organic acids that pull solution pH down. In an 11 L reservoir, pH can fall 0.5–1.0 in 24 hours.

Fix: Add pH-Up (potassium hydroxide solution) drop by drop. 1–2 mL per 10 L, wait 5 minutes, measure again. Test your reservoir twice a day during veg and flower.

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: Gradually add more nutrient (5 mL extra per 10 L per day, wait 24 h, measure, repeat). Check your A+B ratio — usually 1:1, not 1:0.5 as some beginners think.

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. With coco this can happen after 4–6 weeks of flower, especially with "heavy feeder" brands.

Fix: Flush with pH-adjusted water (6.0) and no nutrients. 10 L water per 11 L pot. Between waterings, measure the runoff EC (water draining from the pot). Goal: runoff EC <0.4 mS/cm before you add nutrients again.

Common beginner mistakes

• Forgetting probe storage: pH probes must not be stored dry. Store in KCl solution. Otherwise the glass bulb fails within 3–6 months.
• Too much pH-Up or pH-Down at once: 0.5 mL per 10 L is a whole pH unit. Add drop by drop, not 5 mL at once.
• Measuring EC without temperature correction: EC rises 2% per °C. At 20 °C a solution reads 1.4 mS/cm; at 28 °C the same solution reads 1.55. Premium meters compensate automatically (ATC); budget meters don't.
• Cuttings on a full feed schedule: cuttings have no roots — they can't take up nutrients. EC 0.2–0.4, not 1.4. You'll just burn the roots.