Input EC (feed EC) is the conductivity of the solution you actually apply: source water plus nutrients plus any pH adjusters. It is the dose. It is measured after mixing and pH adjustment, at 25 °C or with temperature compensation.
In practice
Always know your base water EC. Tap water at 0.5 mS/cm plus 1.2 mS/cm of nutrients gives an input EC of about 1.7 mS/cm, but 0.5 of that may be sodium, chloride and bicarbonate that are not useful to the plant. With RO water at 0.02 mS/cm, nearly all the EC is nutrient. Two growers following the same chart can therefore deliver quite different nutrition.
Track input and runoff EC together. Input EC is what you control; runoff EC tells you how the plant and medium responded. Hershkowitz, Westmoreland and Bugbee (2025) found that raising nutrient concentration beyond moderate levels did not improve yield or cannabinoids, so a stable, moderate input EC with steady runoff is a sound default.
Don't confuse with
- Runoff EC: what drains out.
- Additive EC: the EC added by nutrients alone (input minus base water), which some charts quote.
EC (electrical conductivity) measures how well a solution conducts electricity, a proxy for total dissolved salts; growers read it in mS/cm to gauge nutrient strength.pH measures how acidic or alkaline a solution is on a 0–14 scale; in growing it controls nutrient uptake, with soil best near 6.0–7.0 and hydro 5.5–6.5.ATC (automatic temperature compensation) is a meter feature that corrects pH or EC readings for sample temperature, usually referencing EC to 25 °C.mS/cm (millisiemens per centimetre) is the standard unit of EC for nutrient solutions; 1 mS/cm equals 1 dS/m and 1,000 µS/cm.RO water is water stripped of most dissolved salts by reverse osmosis; it has near-zero EC and little buffering, so pH moves easily and Ca and Mg must be added.Runoff is the water or nutrient solution that drains out of the bottom of a container after irrigation; growers test it to see what is happening in the root zone.A cannabinoid is any compound that binds the body's cannabinoid receptors or shares the typical cannabis terpenophenolic structure; the plant-made ones are phytocannabinoids such as THCA and CBDA.Runoff EC is the conductivity of solution draining from the pot; compared with input EC, it shows whether salts are building up or being used up in the root zone.Tap water is municipal or well water used for irrigation; its EC, alkalinity, hardness, sodium and disinfectant vary widely, so it should be tested before use.
