pH for Hydroponics — Canada
Target 5.8–6.2 for almost everything. Drift up over time in most systems. Adjust with commercial pH up/down, never kitchen ingredients. The nutrient-lockout chart and the rules that prevent it.
The short version: Target pH 5.8–6.2 in the reservoir for nearly every hydroponic crop. Check daily in DWC/NFT, at every top-up in Kratky. Adjust with commercial pH up (potassium hydroxide) or pH down (phosphoric acid) — never household vinegar or baking soda. Most leafy-green systems drift upward over time as plants consume nitrate; resetting via partial reservoir change is the right reset. The 5.8–6.2 window keeps every nutrient available; outside it, lockout causes "phantom deficiencies" that adding more nutrients won't fix.
pH is the single most important number in a hydroponic system — more than EC, more than nutrient brand, more than light hours. A correctly-fed plant in the wrong pH starves; a barely-fed plant at perfect pH grows fine. Most new Canadian hydroponic growers fail their first reservoir not from missing nutrients but from never measuring pH. This page is the fix.
Why pH Matters So Much in Hydroponics
In soil, the soil itself acts as a buffer — minerals and organic matter resist pH swings and keep nutrients chemically available across a wide range. In hydroponics, there is no soil. The nutrient solution is what the roots have, and its pH directly controls which forms of each nutrient are present.
A nutrient that is "in the water" is not necessarily one the plant can use. At high pH (above 6.5), iron and manganese precipitate into insoluble forms — the roots can't pull them in. At low pH (below 5.5), calcium and magnesium availability drops sharply. The plant can show classic deficiency symptoms while the solution is technically dosed correctly. That is nutrient lockout, and it's almost always caused by pH drift.
Target pH by Crop
| Crop | Ideal pH | Tolerable range |
|---|---|---|
| Lettuce, leafy greens | 5.8–6.2 | 5.5–6.5 |
| Basil, parsley, mint, herbs | 5.8–6.2 | 5.5–6.5 |
| Tomato | 5.8–6.3 | 5.5–6.5 |
| Pepper | 5.8–6.3 | 5.5–6.5 |
| Strawberry | 5.8–6.0 | 5.5–6.5 |
| Cucumber | 5.8–6.0 | 5.5–6.5 |
| Cannabis (BC legal home) | 5.8–6.2 | 5.5–6.5 |
The Nutrient Lockout Chart
This is the chart every hydroponic grower bookmarks. It shows which nutrients become unavailable as pH drifts out of the central band.
| pH range | What gets locked out | Symptoms |
|---|---|---|
| Below 5.0 | Calcium, magnesium, molybdenum | Brown leaf edges, brittle leaves, deformed new growth |
| 5.0–5.5 | Some Ca, Mg restriction | Mild interveinal yellowing |
| 5.8–6.2 (target) | All nutrients fully available | No lockout symptoms |
| 6.2–6.5 | Iron, manganese starting to drop | Light interveinal yellowing on new leaves |
| 6.5–7.0 | Iron, manganese, zinc heavily locked | Pronounced yellow new leaves with green veins |
| Above 7.0 | Most micronutrients locked; precipitation | Severe deficiency symptoms, stunted growth |
How to Test pH — Drops vs Meter
pH test drops ($10–20)
Pros: Cheap, indefinite shelf life, no calibration, no batteries. Accurate to about 0.2 pH units.
Best for: Kratky and beginner DWC. Daily reads not needed at this resolution.
Digital pH meter ($20–60)
Pros: Accurate to 0.01 pH units, instant reads. Cuts guesswork.
Cons: Needs calibration every 2–4 weeks with pH 4 and pH 7 calibration solutions ($10/year). Probes degrade and need replacement every 1–2 years.
How to Adjust pH Safely
- Test current pH in a small sample taken from the reservoir into a clean cup.
- Pick the direction. Use pH down (phosphoric acid) to lower; pH up (potassium hydroxide) to raise. Wear eye protection — both are caustic concentrates.
- Add a few drops at a time. A single millilitre of pH down can shift a 10 L reservoir by a full unit. Less is more.
- Stir or run the air pump for 60 seconds to mix.
- Re-test. Repeat until you land in 5.8–6.2.
- Never use kitchen acids/bases. Vinegar, lemon juice, citric acid, baking soda — all destabilise the chemistry, feed bacteria, or introduce sodium. Commercial pH up/down is cheap and predictable; use it.
Why pH Drifts and What To Do
pH climbing in DWC / NFT
Normal — plants consume nitrate (negatively charged) and leave the solution slightly alkaline. Adjust down to 5.8 every 1–2 days. If you're chasing it daily, the reservoir wants a full change.
pH falling rapidly
Often a warning sign of root rot — pathogenic bacteria produce organic acids that drop pH. Inspect roots. Slimy brown roots confirm rot — full reservoir change plus root trim plus address temperature/aeration. A falling pH can also mean ammonium-heavy nutrients (some fertilizers) or unflushed organic media.
pH stable but plants showing deficiency
Could be lockout from a temporary drift you missed, or genuine deficiency from low EC, or hard tap water (high pH starting point). Check EC. Adjust pH back into the central band and refresh nutrients. Symptoms typically resolve within 3–5 days.
Frequently Asked Questions
What pH is my Canadian tap water?
Most Canadian municipal tap water is pH 7.0–8.0 — alkaline, well above the 5.8–6.2 target. You will always need pH down when starting a fresh nutrient solution. Some Prairie cities (Calgary, Regina) push pH 8+. Hard water also brings dissolved calcium and bicarbonate that buffer against pH down — you'll use more adjuster than in soft-water cities like Vancouver. RO water solves both problems but adds equipment cost; tap is fine for most home setups if you accept the pH adjustment routine.
How often should I check pH?
DWC and NFT: every 1–2 days, more often during active feeding. Kratky: at setup, every top-up, and once mid-cycle if you're worried. Brand-new systems should be checked daily until you learn the drift pattern; established ones can stretch to a few days.
Can I use citric acid instead of commercial pH down?
Technically yes, in a pinch — citric acid is the food-grade kitchen version of an organic acid that lowers pH. In practice no — citric acid is consumed by reservoir bacteria within hours, so the pH rebounds, and it adds an organic substrate that feeds unwanted microbial growth. Stick to phosphoric acid (commercial pH down). A bottle lasts most home growers a year for around $15.
What pH meter should I buy in Canada?
For hobby use, look for a basic digital pH pen with replaceable electrode, in the $20–40 range from Amazon.ca or a hydro shop. The Apera PH20 and HM Digital PH-200 are reliable and well-reviewed by Canadian growers. Whatever model you pick, buy pH 4.0 and pH 7.0 calibration solution at the same time — a $40 meter with no calibration is worse than a $15 set of drops.
More Hydroponics Guides
Indoor Growing, Calculated
PPFD, EC, electricity — the math your hydroponic system actually needs, free.
Nutrient EC Calculator →