What is the difference between EC and ppm?

EC, electrical conductivity in millisiemens per centimetre, is the direct physical measurement. ppm is EC converted using a scale factor: the 500 scale multiplies by 500, the 700 scale by 700. Always know which scale your meter uses, or the same solution reads two different ppm numbers.

Why does my pen show a different ppm than the chart?

Because feed charts and pens use different ppm scales. A 2.0 EC solution is 1000 ppm on the 500 scale but 1400 ppm on the 700 scale — the solution is identical. Select the scale your pen uses so the converted ppm matches what you read.

Should I add Cal-Mag or pH adjuster here?

This tool doses the nutrient parts you define. Add Cal-Mag as one of the parts if your chart lists it. Adjust pH after mixing and after letting the nutrients dissolve, since adding salts shifts pH on its own.

What EC should my plants run at?

It depends on crop and stage. Leafy greens and seedlings often run 0.8 to 1.6 EC, while fruiting tomatoes or peppers in late growth can take 2.4 to 3.0 EC. Start low, watch the plants, and raise EC gradually rather than shocking them.

Why mix nutrients before checking EC?

EC depends on everything dissolved in the water, including your starting tap-water EC. Add your concentrates, stir, let them dissolve, then measure. If the reading is below target, add a little more solution proportionally; if above, dilute with plain water.

What is the Hydroponics Nutrient Solution Calculator?

Enter your reservoir volume, target EC, and the dose-per-litre strength of each nutrient part to compute exactly how many millilitres of each concentrate to add. Converts between EC and ppm on the 500 and 700 scales for hydroponic and aeroponic growers. It runs free in your browser on Gera Tools, with nothing uploaded.

Hydroponics Nutrient Solution Calculator

Name: Hydroponics Nutrient Solution Calculator
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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Dialling in a hydroponic reservoir means hitting a target nutrient strength without over- or under-feeding. This calculator scales each nutrient part to your reservoir size, reports the total volume of concentrate, and converts your target EC to ppm on whichever scale your meter uses.

How it works

Each part is dosed proportionally to your reservoir volume, and EC converts to ppm with a fixed scale factor:

ml of part   = dose_per_litre × reservoir_litres
total ml     = sum of all parts
ppm (500)    = EC × 500
ppm (700)    = EC × 700

EC is the honest measurement; ppm is just EC multiplied by 500 or 700 depending on the convention your meter follows, which is why two pens can disagree on ppm while measuring the same water.

Worked example: 50-litre reservoir

Two-part formula dosed at 2 ml/L each, target EC 2.0, tap water starting EC 0.3:

Part A: 2 ml/L × 50 L = 100 ml
Part B: 2 ml/L × 50 L = 100 ml
Total concentrate added: 200 ml

Target EC from nutrients alone = 2.0 − 0.3 (tap water EC) = 1.7 EC worth of nutrients to add. If the manufacturer’s chart calls for 2 ml/L to reach 2.0 EC in pure water, use slightly less (roughly 1.7 ml/L) to account for your tap-water baseline — or trim after mixing and measuring.

On a 500-scale pen: 2.0 EC = 1,000 ppm. On a 700-scale pen: 2.0 EC = 1,400 ppm. Same solution, different numbers — always confirm which scale your pen uses.

Target EC ranges by crop and growth stage

EC tolerance varies considerably by species and stage:

Crop / Stage	Target EC (mS/cm)
Seedlings and cuttings	0.5–0.8
Leafy greens (lettuce, spinach, herbs)	0.8–1.6
Fruiting crops — early vegetative	1.2–1.8
Fruiting crops — flowering/fruiting	2.0–2.8
Tomatoes (mature)	2.5–3.5
Strawberries	1.0–1.8
Cannabis (late flower)	2.0–3.0

Always start at the lower end of the range for young plants, new cultivars, or any time you are uncertain, and raise gradually while observing leaf colour and growth rate.

The correct mixing sequence

Mixing order prevents salt precipitation that can block emitters and create nutrient lockout:

Fill the reservoir with your water source.
If using Cal-Mag as a separate additive, add it first and stir thoroughly.
Add Part A, stir until dissolved.
Add Part B, stir until dissolved — never add A and B to each other directly, as concentrated calcium and sulfate salts precipitate on contact.
Add any bloom boosters, silica, or other additionals.
Stir thoroughly and wait 10–15 minutes for salts to fully dissolve.
Measure EC, compare to target.
Adjust pH to your target range (typically 5.5–6.2 for most hydro crops).

Understanding tap-water EC

Most tap water carries some dissolved minerals and therefore a baseline EC of 0.1–0.5 mS/cm. Hard water areas may run higher. This baseline EC is real nutrient content your plants can partially use, but it also means your target EC for nutrient additions should be reduced by your starting tap EC. Some growers prefer to start with RO (reverse osmosis) or rainwater at near-zero EC so they have complete control over the nutrient profile.