Hydroponics Calculators

Nutrient mixing, reservoir sizing, lighting and irrigation timing. 10 calculators for soilless growers. Soil growing sits under Gardening.

Electrical conductivity (EC) mixing works in EC rather than parts per million, and that choice sidesteps a real trap. Two parts-per-million scales are in circulation, the 500 scale and the 700 scale, and a meter reading 1,000 on one reads 1,400 on the other from the identical solution. EC reads the same on every meter ever made. If you do quote parts per million, say which scale, because a grower following a chart written on the other one is off by 40%.

Grow light intensity works in Photosynthetic Photon Flux Density (PPFD), and it pairs every figure with the photoperiod it assumes, which is why its Daily Light Integral column agrees with itself. Many published tables do not. Vegetative growth at 400 to 600 over 18 hours and early flower at 600 to 900 over 12 land on the same daily total, because a plant counts photons per day rather than per second.

Reservoir and top-up pages work from plant uptake rather than tank size. A tank that has lost half its water to transpiration has gained conductivity without gaining a single milligram of nutrient, which is why topping up with plain water is usually right and topping up with fresh solution is usually not.