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Free Hydroponic Nutrient PPM & EC Calculator Culinary & Agriculture
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Free Hydroponic Nutrient PPM & EC Calculator

Convert between EC (mS/cm), Hanna 500, and Truncheon 700 scales, and calculate exact nutrient stock dosing or dilution water needed for target reservoir EC.

🌱 Reservoir Readings & Crop Target

Total tank water volume
Pen meter reading
Goal in EC (mS/cm)

⚡ Multi-Scale Conversion & Adjustment

Electrical Conductivity (EC) -- mS/cm (Millisiemens)
Hanna Scale (PPM 500) -- Parts Per Million (TDS)
Truncheon Scale (PPM 700) --
CF Units (Conductivity Factor) --
Adjustment Action Required --
Estimated Stock Concentrate to Add --
Osmotic Stress / Burn Risk --

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Why EC Is the Only Universal Truth in Hydroponics

Pure water does not conduct electricity. When mineral nutrient salts (Nitrates, Phosphates, Potassium, Calcium, Magnesium) dissolve in water, they disassociate into positive cations and negative anions. A hydroponic meter measures Electrical Conductivity (EC)—the physical ability of those ions to pass an electric current between two electrodes, expressed in milliSiemens per centimeter (( ext{mS/cm})).

The Great PPM Confusion: 500 vs. 700 Scales

No consumer handheld meter can physically measure "parts per million" (PPM) of chemical salts in water. Meters measure EC directly, then multiply by a proprietary conversion factor to simulate a PPM reading:

  • PPM 500 (Hanna / TDS Scale): PPM = EC × 500. Based on potassium chloride (( ext{KCl})) calibration. Standard in the United States. (1.0 EC = 500 PPM).
  • PPM 700 (Truncheon / UK / Australian Scale): PPM = EC × 700. Based on sodium chloride (( ext{NaCl})) calibration. (1.0 EC = 700 PPM).
  • PPM 640 (Eutech Scale): PPM = EC × 640. (1.0 EC = 640 PPM).

The Danger of Confusion: If a recipe calls for "1000 PPM" and you use a 500-scale meter thinking it is a 700-scale meter, you will overfeed your plants by 40%, causing catastrophic salt toxicity and root burn!

Frequently Asked Questions

Why should I always calibrate my meter in EC rather than PPM?

Because EC is an absolute international physical standard based on electrical resistance. 1.0 mS/cm is identical on every meter on Earth. PPM is an artificial mathematical conversion that causes massive confusion between different meter brands.

What does it mean if reservoir water level drops but EC rises?

This means your plants are drinking pure water faster than they are consuming nutrient salts (transpiration exceeding nutrient demand). This happens under high temperatures or low humidity. Top off the reservoir with pure water to bring EC back down to target.

What does it mean if reservoir water level drops and EC drops?

This indicates your plants are feeding aggressively, extracting mineral ions faster than water. This is a sign of healthy vigorous growth—you can safely raise your nutrient target EC by 0.2 mS/cm on your next feeding.

What is the ideal pH range for hydroponic nutrient uptake?

The sweet spot for soilless and recirculating hydroponics (DWC, NFT, Rockwool) is strictly 5.5 to 6.2 pH. Above 6.5 pH, Iron and Phosphorus precipitate out of solution and become unavailable. Below 5.2 pH, Calcium and Potassium uptake is blocked.

Why must A and B nutrient concentrates never be mixed together in pure form?

Part A contains concentrated Calcium Nitrate; Part B contains concentrated Magnesium Sulfate and Phosphates. Mixing them together undiluted causes the calcium and sulfate to react instantly, precipitating into insoluble solid Gypsum (Calcium Sulfate) that plants cannot absorb.