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Protected Cultivation & Nursery Calculators

Hydroponic & Fertigation EC/pH Calculator

Calculate grams of fertilizer salt for a target nutrient ppm, the acid needed to bring down pH, and the ppm equivalent of your target EC.

Enter your details

ppm (mg/L)

Optional – shown as a ppm reading for TDS meters.

mS/cm

From a water test. Optional – for acid dosing.

mg/L CaCO₃

About 40–60 mg/L gives a solution pH near 5.8–6.2.

mg/L CaCO₃

Please note: This calculator provides a mathematical estimate based on the values entered. Recommended agricultural application rates can vary by crop, soil, product formulation, location and official agricultural guidance. Check the product label and local agricultural recommendations before application.

Mixing a nutrient tank? Enter the tank volume, pick the fertilizer salt and the ppm of the nutrient you want, and get the grams to dissolve. Add your water's alkalinity to get the millilitres of acid that bring the solution into the ideal pH range.

About the Hydroponic & Fertigation EC/pH Calculator

Hydroponic and fertigation recipes are written in ppm (milligrams per litre) of each nutrient – for example 150 ppm nitrogen, 50 ppm phosphorus, 200 ppm potassium. Fertilizer bags contain salts, each carrying only a share of a nutrient. This calculator converts one into the other for any tank size.

It also handles the most common pH problem. Most borewell water in India is alkaline: its bicarbonates push the solution pH above 7, where iron, manganese and phosphorus become unavailable. Adding the right amount of acid neutralises most of this alkalinity and brings pH into the ideal 5.8–6.5 range.

  • Salt – grams = target ppm × litres ÷ (nutrient % × 10).
  • Acid – based on the alkalinity to remove, measured in mg/L of CaCO₃ from a water test.
  • EC – converted to the ppm shown by TDS meters on the 500 and 700 scales.

When a salt supplies two nutrients (like potassium nitrate), calculate it for one nutrient, then count what it adds of the other before dosing the next salt.

How to use the Hydroponic & Fertigation EC/pH Calculator

  1. 1 Enter the tank volume. For stock solutions, use the stock tank volume and multiply the recipe ppm by your injector's dilution ratio.
  2. 2 Pick the fertilizer salt and the nutrient you are dosing, and enter the target ppm.
  3. 3 For pH, enter your water's alkalinity from a water test and choose the acid.
  4. 4 Optionally enter the target EC to see the ppm your TDS meter should read. Press Calculate.

The formula we use

Salt (g) = Target ppm × Tank (L) ÷ (Nutrient % × 10)
Acid (ml) = (Alkalinity − Target alkalinity) ÷ 50 × Acid factor × Tank (L) ÷ 1,000
TDS (ppm) ≈ EC (mS/cm) × 500 or × 700

The acid factor is the millilitres of acid that neutralise 50 mg/L CaCO₃ (1 meq/L) in 1,000 litres: about 77 ml of 60% nitric acid, 68 ml of 85% phosphoric acid or 27 ml of 98% sulphuric acid.

Worked example

You want 150 ppm nitrogen from calcium nitrate (15.5% N) in a 1,000 litre tank. Your water has 200 mg/L alkalinity and you use 60% nitric acid.

  1. Calcium nitrate = 150 × 1,000 ÷ (15.5 × 10) = 967.7 g.
  2. Acid = (200 − 40) ÷ 50 × 77 = 3.2 × 77 = 246 ml of nitric acid.
  3. A target EC of 2.0 mS/cm reads about 1,000 ppm on a 500-scale TDS meter.

Note that the nitric acid also adds nitrogen – about 14 ppm N per meq/L – so reduce the nitrogen from salts a little.

Things to keep in mind

  • Add acid to water, never water to acid. Wear gloves and eye protection; strong acids cause severe burns.
  • Keep calcium and sulphate/phosphate apart in concentrated stock (A and B tanks), or they form insoluble precipitates.
  • Always measure. Check the final EC and pH with calibrated meters and adjust in small steps.
  • Salt grades differ. Use the nutrient % printed on your bag if it is different.

Frequently asked questions

How do I convert ppm to grams of fertilizer?

Grams = ppm × litres ÷ (nutrient % × 10). For 100 ppm potassium from potassium sulphate (41.5% K) in 500 litres: 100 × 500 ÷ 415 = 120.5 g.

What pH should a hydroponic solution have?

Most crops do best between pH 5.8 and 6.5, where all nutrients stay available.

What is the difference between the 500 and 700 ppm scales?

TDS meters convert EC to ppm with different factors. The same 2.0 mS/cm solution reads 1,000 ppm on a 500-scale meter and 1,400 ppm on a 700-scale meter, so always note which scale your recipe uses.

Last updated . Spotted a mistake or need a unit we don't support? Tell us.