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.

Hydroponics Nutrient Solution Calculator

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.

Example and tips

For a 50 litre reservoir with a two-part formula dosed at 2 ml/L each, you add 100 ml of part A and 100 ml of part B, 200 ml total. A 2.0 EC target reads 1000 ppm on a 500-scale pen. Always add nutrients to water, never the reverse, stir between parts so salts do not precipitate, and confirm the final EC with your meter before setting pH. Tap water already carries some EC, so your additions may need trimming to land exactly on target.