pH, EC and Water Temperature in Hydroponics

3 min read

A pH pen and EC meter beside a hydroponic reservoir with an aquarium thermometer

In soil you can get away with rough pH, ballpark nutrients and the odd neglected day. In hydro, pH, EC and water temperature are daily non-negotiables — there’s no medium buffering your mistakes, so the roots taste every change immediately. Get these three right and hydro hums; get them wrong and it turns on you in hours.

The short version:

  • pH 5.5–6.5 (most aim 5.8–6.0) — lower than soil, and it drifts fast
  • EC — start low (~0.8–1.0 for young plants), build up to 1.5–2.0 in flower
  • Water temp 18–21°C — above 22°C oxygen drops and root rot moves in
  • Mix nutrients A-then-B into the water; never combine them neat
  • Daily checks aren’t enthusiasm — they’re maintenance, like checking oil

Want the full breakdown? Keep scrolling.

pH — narrower and faster than soil

Hydro runs at pH 5.5–6.5, most growers aiming 5.8–6.0 — lower than soil’s 6.0–7.0, because dissolved nutrients are most available to roots in that band. Drift above 6.5 and iron and manganese lock out; below 5.5 and calcium and magnesium go unavailable. The window’s narrower than soil’s because there’s no organic buffer holding it steady — and hydro nutrients are themselves slightly acidic, so the solution acidifies itself over time with nobody counteracting it. That’s why the Scientist’s reservoir crashed from 6.5 to 4.8. Daily checking is maintenance, not obsession — like checking the oil in a car: you do it so the engine doesn’t seize. A reliable pH pen (DIG stock the HM Digital PH-80, which reads pH and temperature) plus pH Up and Down, two minutes each morning.

EC and water temperature

EC (electrical conductivity) measures how strong the feed is. Start low — a young plant in DWC wants barely-there EC around 0.8–1.0, a mature plant in peak flower maybe 1.5–2.0 — and build up gradually while watching the plant, because in hydro the roots taste every molecule at once: the Chef doubles the dose and burns every root tip in a week. Also mix correctly — hydro nutrients come in A and B bottles because certain minerals turn to useless chalk if combined neat, so A into the water, stir, then B, and measure with an EC pen after. Water temperature 18–21°C is the silent killer if ignored: above 22°C warm water holds less dissolved oxygen and pathogens like pythium thrive, so root rot follows — the Hot Tub at 24°C under the lights. Keep the reservoir off the tent floor, insulated, and consider an aquarium chiller in summer (insurance, not luxury). Below 16°C is too cold — uptake stalls — but in a warm tent, too-hot is the common problem.

What else should I know?

Check your starting water before you mix anything — Dublin tap is already ~0.3–0.4 EC, so you’re not starting from zero, and hard-water (limestone) areas carry calcium that fights your pH adjustments, where reverse-osmosis filtration removes the variable. And keep the reservoir clean and changed weekly — topping up skews the nutrient ratios even when the EC reads fine, so a full change resets the chemistry every week (DIG stock pens, meters and chillers). These three numbers, checked daily, are the price of admission to hydro. If checking them every morning sounds like too much, that tells you something useful — soil might suit you better.

FAQ

What pH should hydroponic cannabis be? 5.5–6.5, with most growers targeting 5.8–6.0. It’s lower than soil and drifts quickly, so check and adjust the reservoir daily.

What EC should I run in hydro? Start gentle — around 0.8–1.0 for young plants — and build to roughly 1.5–2.0 in peak flower. In hydro the roots feel the full strength immediately, so increase gradually.

Why does reservoir temperature matter so much? Above about 22°C the water holds less oxygen and root-rot pathogens thrive, so warm reservoirs cause brown, slimy roots within days. Keep it 18–21°C, off the floor and insulated.

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