CF Meters

CF meters usually read in milliSiemens or CF units but for the grower it is simply a matter of getting the decimal point in the right place. As a rule of thumb, it can be said that a good conductivity level for most purposes would be 2.0 milliSiemens (expressed as 2.0 mS/cm2). We can call this a standard working solution. Therefore: standard working solution = 2.0mS = 2,000S = 20 CF units




EC
Conductivity is sometimes expressed as EC (Electrical Conductivity). Units of EC are now identical to CF units.

Parts per Million

Conductivity is sometimes expressed in terms of parts per million (ppm). One gram of any salt, dissolved in a litre of water will make a solution containing 1000 ppm of that salt. However, different salts have a different capacity to conduct electricity so two solutions made with different salts could both be 1000 ppm, but have quite different readings on a CF meter. It is therefore not possible to make an exact conversion from parts per million to CF units, however as most nutrients solutions have approximately the same ration of constituent salts we can make an approximate conversion.

1mS = 10 CF units  640 ppm

Therefore

Standard working solution = 20 mS = 20 CF  1280 ppm