EC, PPM, and TDS for Hydroponics — Canada
What the three nutrient-strength scales actually measure, the conversion chart between them, the target ranges by crop, and how EC drift tells you exactly what your plants are doing in the reservoir.
Short version: EC = electrical conductivity = nutrient strength in a hydroponic solution. PPM and TDS are EC converted to "parts per million" estimates by a factor — PPM-500 (North America) and PPM-700 (Europe) exist and disagree on the same solution. Just learn EC and ignore the confusion. Target 0.8–1.4 EC for leafy greens, 2.0–3.0 EC for fruiting tomato/pepper. Rising EC means plants are drinking water faster than nutrients; falling EC means the opposite. Test with a $25 digital pen.
EC is the second number every hydroponic grower learns to read (pH is the first). It tells you the strength of the nutrient solution — how much dissolved fertilizer is in there. Get EC right and your plants grow at their genetic potential; get it wrong in either direction and you'll see tip burn, slow growth, or both. This page covers what EC is, the unit-of-measurement mess that is PPM, target strengths by crop, and how to read EC drift like a diagnostic tool.
What EC, PPM, and TDS Actually Measure
EC (electrical conductivity) is the direct measurement — how well the solution conducts electricity. Dissolved mineral salts (the active ingredients in hydroponic nutrients) carry charge; pure water carries almost none. Stronger nutrient solution = better conductor = higher EC. Reported in mS/cm (milliSiemens per centimetre) or uS/cm (microSiemens). 1.0 mS/cm = 1,000 uS/cm.
PPM (parts per million) and TDS (total dissolved solids) are derived from EC by multiplying by a conversion factor. They are estimates, not direct measurements. Two scales exist:
- PPM-500 scale (North America): 1.0 EC × 500 = 500 PPM. Used by most US/Canada-targeted meters and recipes.
- PPM-700 scale (Europe): 1.0 EC × 700 = 700 PPM. Used by most European meters and recipes.
Same solution. Two different PPM numbers. Same EC. This is why most experienced growers stick to EC and avoid PPM entirely — one scale, no confusion. If you must use PPM, always know which scale your meter is reading on.
The Conversion Chart
| EC (mS/cm) | PPM-500 (US/Canada) | PPM-700 (EU) | Use case |
|---|---|---|---|
| 0.4 | 200 | 280 | Seedlings, microgreens |
| 0.8 | 400 | 560 | Young leafy greens |
| 1.2 | 600 | 840 | Mature lettuce, herbs |
| 1.6 | 800 | 1120 | Mature kale, bok choy; tomato seedling |
| 2.0 | 1000 | 1400 | Young tomato/pepper |
| 2.5 | 1250 | 1750 | Flowering tomato/pepper |
| 3.0 | 1500 | 2100 | Fruiting tomato; max for most crops |
Target EC by Crop and Stage
| Crop | Seedling | Vegetative | Flower / Fruit |
|---|---|---|---|
| Lettuce, leafy greens | 0.6–0.8 | 0.8–1.4 | n/a (harvest before bolt) |
| Basil, herbs | 0.6–0.8 | 1.0–1.6 | 1.4–1.8 if flowering |
| Strawberry | 0.8–1.0 | 1.2–1.5 | 1.4–1.8 |
| Tomato | 0.8–1.0 | 1.6–2.4 | 2.4–3.0 |
| Pepper | 0.8–1.0 | 1.4–2.0 | 2.0–2.8 |
| Cucumber | 0.8–1.0 | 1.6–2.0 | 2.0–2.5 |
Reading EC Drift — What the Numbers Mean
How EC changes between top-ups tells you what the plants are doing:
EC climbing — plants drinking water faster than nutrients
Common in hot rooms or when EC is set too high for the crop. Solution: top up with plain pH-adjusted water to dilute back to target. If it keeps climbing after top-ups, the base EC is too strong — reduce next refresh.
EC falling — plants eating nutrients faster than water
Normal in active vegetative growth and fruiting stages. Solution: top up with weak nutrient mix to maintain strength. A steady downward trend is the healthiest pattern; the plant is feeding well.
EC stable — balanced uptake
Plants are taking water and nutrients in roughly the same ratio as the solution provides. Top up with the same strength nutrient as your base. This is the easy state to be in.
EC Troubleshooting
Lettuce tip burn (brown crispy edges)
EC too high — over 1.6 for lettuce. Calcium uptake gets disrupted and leaf tips die back. Dilute the reservoir down to 1.0–1.2 EC and watch new growth. Old damaged leaves don't recover; new ones come in clean.
Slow, pale, nitrogen-deficient looking growth
EC too low — plants under-fed. Boost reservoir strength incrementally, give a few days, watch the response. Pale isn't always EC — could be pH lockout; check pH first.
EC reading way off from expected
Calibrate your meter against EC 1.41 calibration solution. Probes degrade over time. If the calibration check is off, the meter has been giving false readings all along.
High starting EC from tap water
Some Canadian tap water already reads 0.3–0.6 EC before any nutrient is added — minerals from the source water. Subtract this baseline when you mix; otherwise your target strength is artificially low. RO water (~0 EC) makes math easier but is expensive equipment.
Frequently Asked Questions
Do I need both an EC meter and a pH meter?
For Kratky leafy greens, you can get away with just pH drops — EC is hard to abuse on short-cycle lettuce. For DWC or any fruiting crop, both meters are worth the $40–80 total. Combo pH+EC pens exist but the EC element in budget combos drifts faster than separate pens; if budget is tight, buy two separate $20 pens.
Why do nutrient bottles give different ratios?
Different manufacturers, different formulations, different target stages. The label rate is a starting point. Mix to the label, measure resulting EC, and adjust to your target. For most home crops, label rates are too strong — start at half-strength and work up.
Can I run different crops at the same EC?
Yes if their target ranges overlap. Lettuce and basil both thrive at 1.0–1.2 — same bin works. Tomato (2.0+) and lettuce (1.2) don't — running together at compromise EC underfeeds the tomato and burns the lettuce. Separate bins for crops with very different EC needs.
How accurate are cheap Canadian Amazon EC meters?
Good enough for home use, with calibration. A $20 EC pen calibrated monthly reads within ±0.1 of laboratory accuracy — well within what hydroponic crops can tolerate. The expensive Bluelab and Apera meters offer better durability and faster reads, not dramatically better accuracy. Calibrate whatever you have.
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