What does pH measure, and why does it run the show for nutrition?
pH is a logarithmic scale (0–14) that tells you how acidic or alkaline your solution or substrate is. In the root zone, every nutrient has a pH window where it stays soluble and available. Outside that window the nutrient is still in solution — the plant just can't take it up. That's nutrient lockout.
The form of available nitrogen also shifts with pH: at low pH you get more ammonium (NH4+), which the plant can only tolerate in limited amounts; the bulk of the N it uses best is nitrate (NO3-). So the target range isn't just 'not too acid, not too alkaline' — there's a precise technical window per substrate.
- Hydro (pure solution): target 5.6–5.8; safe range 5.5–6.0
- Coco (fertigated): 5.8–6.2
- Soil (with organic matter): 6.0–6.5
- Seedling: hydro 5.8–6.0; coco 6.0–6.3; soil 6.0–6.2 (NC State, Volcani Center, Truog chart)
What does EC measure — and what does it NOT tell you?
Electrical conductivity (EC) measures total dissolved salts. More salts = more current between the electrodes = higher EC. What EC does NOT tell you is which salts those are: tap water with excess sodium can read high EC while still being low on usable calcium.
EC is a concentration guide, not a composition read. That's why a complete, balanced fertilizer changes the math: when you add the correct dose, you know you're adding the right ions, and the resulting EC actually reflects useful concentration.
- Seedling: EC 0.4–0.5 (200–250 PPM) in coco and hydro; plain water in amended soil
- Veg: EC 0.8–1.6 depending on substrate and week
- Bloom: EC 1.4–2.2 at peak (hydro/coco); somewhat lower in soil
- Rule of thumb: doubling EC does not double yield — past a certain point you're just adding salt
Why is an uncalibrated meter the most common hidden cause of problems?
pH electrodes drift over time: the glass membrane wears out, the reference solution gets contaminated, or the probe dries out and loses its baseline. A meter reading 0.3 units high means you 'adjust' to pH 6.0 when you're actually at 6.3 in hydro — enough to start locking out iron and manganese.
Calibrating with standard buffer (pH 4.0 and 7.0 or 6.86) takes 3 minutes and delivers the highest return on time invested of any step in your feeding routine. Same goes for EC: conductivity electrodes build up a salt film and need cleaning and calibration with a standard solution.
How do you adjust pH when you're working with hard tap water?
Tap water across much of Argentina runs alkaline: pH 7.5–8.5 and hard (high calcium and bicarbonates). That means you'll almost always need to bring pH DOWN after mixing your nutrient solution.
When should you check and adjust EC?
EC in your reservoir shifts over time: in warm weather the plant drinks more water than it consumes salts (EC climbs); in cool weather it consumes more salts than water (EC drops). Measuring EC and pH together and topping off with plain water or fresh solution as needed keeps the system stable without dumping the whole reservoir.
- EC climbed above target: top off with plain water (no nutrients)
- EC dropped below target: top off with solution at the target concentration
- pH drifted out of range: adjust pH and re-check EC — pH adjusters also contribute salts
- Full reservoir change every 7–10 days in recirculating hydro to prevent sodium and bicarbonate buildup
