- Translate µS/cm, mS/cm and meter ppm.
- Calibrate and sample consistently.
- Interpret EC alongside water level and crop conditions.
EC and meter-ppm converter
Meter ppm = EC (mS/cm) × meter factor.
500-scale meter ppm: 800; 640-scale (TDS) meter ppm: 1,024; 700-scale meter ppm: 1,120; EC (µS/cm): 1,600
These are meter conversions, not measured elemental nutrient concentrations. 640 is the factor some general-purpose TDS meters and Penn State’s water-test guidance use; check which scale your meter applies.
01 / Record the measured quantity
EC expresses how readily solution conducts electricity. In hydroponic work, mS/cm and dS/m are numerically equivalent; 1 mS/cm equals 1,000 µS/cm. By instrument-manufacturer convention, a “500 scale” meter reports approximately EC in mS/cm × 500 as ppm and a “700 scale” meter uses × 700; Penn State’s irrigation-water guidance estimates TDS with × 640, and some general-purpose meters offer that setting.
Thus 1.6 mS/cm can display 800 ppm or 1,120 ppm on correctly functioning meters using different factors. Those numbers are not measurements of nitrogen or of a known fertilizer mass. Record EC directly, the reference temperature or automatic temperature compensation setting, and the meter model.
Reading: Electrical Conductivity and pH Guide for Hydroponics ↗ · Interpreting Irrigation Water Tests ↗
02 / Build a repeatable sampling routine
Use fresh calibration standards and follow the probe manufacturer’s procedure. Keep the original standard bottle uncontaminated by pouring a small separate aliquot. Rinse between samples, allow readings to stabilize and record the temperature.
pH measures acidity; alkalinity measures resistance to pH change. Two water sources with the same starting pH may require very different acid additions. Calibrate the pH meter using appropriate buffers that bracket the working range; Missouri’s guidance illustrates pH 4 and 7. Store the electrode in the specified solution, not dry or in distilled water.
- Sample a mixed reservoir before adjustment and label the location and time. Avoid a concentrated dosing plume or a stagnant corner.
- Inspect and calibrate the instruments. Check an independent standard if readings conflict with the crop or prior log.
- Measure temperature, EC and pH, waiting for stable results. Keep units alongside every value.
- Make one recorded adjustment, circulate, then remeasure. Do not keep adding correction while the previous dose is still mixing.
Reading: Hydroponic Nutrient Solutions (G6984) ↗ · Interpreting Irrigation Water Tests ↗
03 / Read paired trends
Water level and EC belong together. Falling level with rising EC suggests concentration by water loss; falling level with falling EC suggests the solution’s conductivity is being depleted relative to water. Neither pattern identifies an individual ion.
If EC is stable but growth deteriorates, inspect roots, temperature, light, pH and the history of selective nutrient uptake. Sodium or chloride can accumulate while useful nutrients decline. A fresh solution or laboratory ion analysis may be needed even when the meter number looks familiar.
| Reading | Equivalent | What it tells you |
|---|---|---|
| 1.6 mS/cm | 1,600 µS/cm | Measured conductivity. |
| 800 ppm on 500 scale | 1.6 mS/cm | A conductivity conversion. |
| 1,120 ppm on 700 scale | 1.6 mS/cm | The same conductivity on a different scale. |
| 1,024 ppm on 640 scale | 1.6 mS/cm | The same conductivity on a third factor, the one Penn State uses for water tests. |
| 117 mg/L N | 117 elemental N ppm approximately | A nutrient-specific concentration, calculated or analyzed. |
Reading: Hydroponic Nutrient Solutions (G6984) ↗ · Electrical Conductivity and pH Guide for Hydroponics ↗
04 / Use a crop-specific operating band
Choose targets from a crop and method reference and include the growth stage. Seedlings, mature leafy crops and heavily fruiting tomatoes should not be forced to share one number because they use the same pump. Source-water EC also contributes to the final reading.
Create a log row with date, volume, temperature, EC, pH, calibration date, addition and follow-up reading. Use the converter below to translate historical logs, then adopt EC as the common unit.
FIELD QUESTIONCan you convert EC directly into the grams of a new fertilizer to add?
No. Different ions and mixtures contribute differently to conductivity. Use the product’s composition and recipe, then verify the mixed solution with the meter.
Parts & buying criteria
Build your own parts & cost worksheet →
Showing nutrient film technique. Quantities describe the teaching model. Specify real working volume, support, fittings and instruments for your installation.
01Reservoir1 · illustrated quantity+
Holds the recirculating nutrient solution. This is the common sampling and refill point for both channels.
Inspect: In cutaway view, compare the water surface with the pump intake. The drawing leaves room above the water; it does not specify a working volume.
Maintain: Record the level before adding water. Inspect the cover, clean accessible deposits and keep the intake submerged during use.
Opaque, cleanable container rated by its manufacturer for the intended use; accessible lid and drain.
Check size, materials and operating conditions with your chosen supplier before ordering.02Pump & supply1 · illustrated quantity+
Lifts solution from the reservoir to the channel inlets. Cyan packets indicate the direction of delivery.
Inspect: Follow the rising supply pipe and its branch to each channel. Both inlets need an observable supply.
Maintain: Disconnect power before opening the pump. Inspect its inlet screen and confirm both branches flow after reassembly.
Compare the pump curve at the installed lift and pipe resistance; include service access and replacement availability. Supply the pump, timer and any air pump through ground-fault protection (GFCI/RCD), keep plugs and cord connections above the water line with a drip loop, and switch off and unplug before reaching into the solution.
Check size, materials and operating conditions with your chosen supplier before ordering.03Growing channels1 · illustrated quantity+
Contain the shallow stream beneath the plants and guide it toward the return.
Inspect: Open the cutaway to find the channel floor beneath the roots. The slope is exaggerated for reading.
Maintain: Look along each channel for ponding, debris or an obstructing root mat; inspect the outlet before changing the pump.
Removable covers, supported slope, smooth cleanable surfaces and outlets accessible with plants in place.
Check size, materials and operating conditions with your chosen supplier before ordering.04Plant baskets6 illustrated · illustrated quantity+
Bridge the opening in the channel cover while allowing roots to pass through.
Inspect: In exploded view, the baskets lift above the channels. The open slats reveal the relationship between support and roots.
Maintain: Check that each rim sits securely and that roots are not pinched at transplanting or inspection.
Match the basket rim and hole diameter; allow removal without damaging adjacent plants.
Check size, materials and operating conditions with your chosen supplier before ordering.05Support mediumFor 6 baskets · illustrated quantity+
The illustrated expanded clay supports the seedling in its basket. The channels are not filled with aggregate.
Inspect: Select the brown pebbles and separate the basket in exploded view. Media texture is simplified.
Maintain: Remove loose particles before installation. Inspect whether the starter plug stays appropriately moist.
Select a stable grade that stays in the basket; compare water retention, dust and cleaning requirements.
Check size, materials and operating conditions with your chosen supplier before ordering.06Gravity return1 · illustrated quantity+
Collects channel outflow and brings it back to the reservoir without a second pump.
Inspect: Trace the low ends of both channels into the common return. Inspect the full path before assuming the circuit is clear.
Maintain: Remove obstructions and check for leaks. Test drainage with the pump off during commissioning.
Removable unions, supported pipe and sufficient drain capacity under the actual installation conditions.
Check size, materials and operating conditions with your chosen supplier before ordering.Evidence beside the lesson.
Source checks: September 2026. The geometry, inspection exercises and worksheets are original teaching material. The named organizations have not endorsed or reviewed this site.
Published recipe rates and planning ranges retain their source context. Calculator equations are accounting tools; they do not predict uptake, yield, toxicity or safe stocking. Model dimensions, water speeds, roots and fish counts are illustrative. Verify species, crop, source water and product labels for a real system.
- Oklahoma State University ExtensionElectrical Conductivity and pH Guide for Hydroponics ↗
Water analysis, salinity, pH and monitoring.
- Penn State ExtensionInterpreting Irrigation Water Tests ↗
Distinguishing alkalinity, pH, salts and source-water problems.
- University of Missouri ExtensionHydroponic Nutrient Solutions (G6984) ↗
Solution preparation, elemental nutrition and measurement.
The next useful connections.
Nutrient mixing: from grams to elemental ppm
Scale two documented fertilizer examples, read the bag analysis and calculate what actually enters the final solution.
Interactive tool · 6 min + guided practice →Source waterSource water and alkalinity
Read a laboratory report, distinguish equivalent units from elemental nutrients and prepare water deliberately.
6 min + guided practice →Buying guidesChoosing EC and pH meters: range, resolution, calibration, probes
An EC or pH meter is bought against the solution band you must hold and the calibration routine you will keep, not against the digits on its display.
Interactive tool · 8 min + guided practice →Nutrients & mixingAdjusting pH in hydroponics: acids, bases and alkalinity
The pH reading tells you which way to push a solution; the water’s alkalinity tells you how hard, and most adjusters leave a nutrient behind.
6 min + guided practice →