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Comenzar gratisEC vs. TDS: What's the Difference?
EC (Electrical Conductivity) measures how well your nutrient solution conducts electricity — the more dissolved minerals it contains, the more conductive the water. The unit is mS/cm (millisiemens per centimeter).
TDS (Total Dissolved Solids) expresses the same information in ppm (parts per million) — how many solids are dissolved per liter of water. Most meters simply convert EC using a factor and display ppm.
Your meter always measures EC — TDS in ppm is just a conversion. Depending on the manufacturer, a factor of 0.5 to 0.7 is used, which is why two meters can show different ppm values for the same solution. EC is the more reliable unit.
Why EC Matters More Than PPM
EC is the industry standard — and for good reason. While ppm values vary significantly depending on the manufacturer's conversion factor, EC always stays consistent. An EC of 1.8 mS/cm means the same thing on every meter.
When comparing grow logs, following forum recipes, or talking to other growers: use EC. It prevents confusion and avoids errors from incompatible conversions.
Hanna meters use factor 0.5 (500 scale), Truncheon meters factor 0.7 (700 scale). So 1.0 EC equals either 500 or 700 ppm — depending on the device. EC bypasses this problem entirely.
Optimal EC Levels by Growth Stage
Your plants' nutrient needs change significantly depending on the growth stage. Seedlings are sensitive and need little — during flowering, plants require much more. A rough guide:
Young plants have an underdeveloped root system. Too-high EC causes nutrient stress and burned root tips. Start low, increase slowly.
During vegetative growth the plant builds biomass and can process more nutrients. Nitrogen (N) is especially important in this phase.
During flowering, demand for phosphorus (P) and potassium (K) rises. Many growers gradually increase EC up to 2.5 mS/cm. Above 3.0 EC it becomes too much for most plants.
How to Measure EC & TDS Correctly
An affordable combo meter for EC/TDS/pH is perfectly sufficient for beginners. More important than the device is correct handling:
- Calibrate the meter before each use — use EC calibration solution (1.413 mS/cm)
- Rinse and dry the electrodes after measuring — deposits falsify the reading
- Measure at room temperature (20–25 °C) — cold water shows falsely low EC readings
- Record results regularly — spot trends before problems become visible
For every 1 °C rise in temperature, EC increases by about 2%. Modern meters have automatic temperature compensation (ATC) — make sure it's enabled.
Common EC & TDS Mistakes
Most nutrient problems in hydroponics don't come from wrong products, but from uncontrolled EC values. These are the most common mistakes:
EC too high (nutrient burn): The plant can no longer absorb water because the concentration in the solution is higher than inside the plant itself. Symptoms: brown leaf tips, wilting despite moist substrate.
EC too low (nutrient deficiency): Plants grow slowly, leaves yellow. This often happens when topping off the reservoir with plain water without adding nutrients.
Plants absorb more water than nutrients. When you top off with plain water, EC in the reservoir automatically rises. Always check EC after topping up and adjust with fresh nutrient solution if needed.
Frequently Asked Questions
EC measures electrical conductivity in mS/cm, TDS shows dissolved solids in ppm. Both measure the same thing — your meter measures EC and converts it internally to ppm. Different manufacturers use different factors (0.5 or 0.7), which can lead to different ppm readings for the same solution.
A universal guideline is around 800 ppm (1.6 EC) for the vegetative phase. Seedlings sit at 400–600 ppm (0.8–1.2 EC), flowering plants at 1000–1250 ppm (2.0–2.5 EC). Exact target values depend on the plant species.
EC is manufacturer-independent and always consistent. PPM values can vary widely depending on the device and conversion factor. If you follow recipes from books or forums, make sure you know which ppm scale the author used — or simply switch to EC.
Partially drain the reservoir and top up with pH-adjusted water (without nutrients) until the desired EC is reached. With severe nutrient burn, a complete reservoir change with freshly mixed nutrient solution may be necessary.
Daily measurements are recommended during active growth phases. At minimum, check at every reservoir top-up and at any sign of nutrient issues (discoloration, growth stall). Logging your values helps you catch deviations early.