Parts per million (PPM), and Electrical Conductivity (EC), both the same thing, two different units of measurement.

Americans tend to use PPM more often, and europeans use EC more often.

You need a TDS electronic pen reader (Total dissolved salts) which tell you the PPM (parts per million) of the TDS of the water.

This is how you know how strong your nutrient strength is.

Roughly 500ppm equals 1 EC. therefore, 300ppm equals .6 EC, 250ppm equals .5 EC.

tap water is normally about 300ppm, when you add nutrients- obviously the ppm will raise.