Conductivity is measured using a conductivity meter. These contain a micro-processor and are therefore fairly expensive, but are essential in accurately maintaining the nutrient solution.

There are three different scales for measuring the conductivity level:

CONDUCTIVITY FACTOR (C.F.)

C.F. is the most common form of measurement and is used throughout this guide. The conductivity factor is a scale of 0 — 100, with 0 having no nutrients and 100 being maximum strength.

ELECTRO CONDUCTIVITY (E.C.)

This scale is calculated in Millisiemens and measures the amount of nutrients to the square centimetre.
The relationship between E.C. and C.F. readings is simply a change of the decimal point (ie: E.C. 2.0 = C.F.20).

TOTAL DISSOLVED SALTS (T.D.S.’)

T.D.S. is less commonly used. It is a measurement of the actual amount of nutrients in the solution, calculated in parts per million.

The table below shows the relation between the three scales.

So, 10 x C.F. units (C.F. 10) = 1 x E.C. unit (E.C. 1.0) = 700 parts per million (700 P.P.M.)