Chapter Seven: Testing nutrient solutions

The secret behind obtaining consistently good results from a hydroponic system lies in two simple tests of the nutrient solution. I will explain these two types of test carefully because once you have an understanding of them, you will have a complete basic knowledge of how to grow hydroponically. The first test is a simple measurement of the strength of the nutrient solution. The strength of the solution is measured by its conductivity factor, and we refer to this as the CF (Conductivity factor) or EC (Electrical conductivity) measurement.

The principles behind taking a CF measurement of your nutrient solution are quite straightforward. Water conducts electricity in the same way that the copper wires running through a house conduct electricity to supply lights and power outlets. This is why it is unwise to operate electrical appliances in damp or wet situations. The water may conduct the electrical current so that you receive an electric shock. Water conducts electricity, because it is full of impurities. There are a number of common elements which are readily dissolved in water producing salts as well as the microscopic particles of all sorts of compounds that we generally call 'dirt’, which are easily suspended in water. Totally pure water itself, will not conduct electricity. How well water will conduct electricity can be measured by an inexpensive and readily available device, the CF meter. This meter basically consists of two electrodes which are placed in the water to be measured.

When switched on, an electronic current tries to pass from one electrode, through the water to the other electrode. The meter has a digital display which will tell you how much electric current is flowing between the electrodes, resulting in the CF measurement. So if a CF meter probe is placed in pure water and switched on, little or no electricity will flow so the meter will produce a readout of zero. Now remember back to the jug of water and common salt we used earlier to produce salt crystals. If a very small amount of this salt solution is added to a container of pure water and the CF meter is used to test it, you will get a reading. The more of the salt solution that is added to the water the higher the CF reading will become.

The nutrient mixture used for hydroponic growing is not very different from a mixture of common salts for the purposes of a CF reading. It is derived from many different elements, but, when you mix them with water they have the same electrical response as common salt mixed with water. The stronger the solution, the more electricity will flow and the higher the reading you will get on a CF meter. The CF scale on hydroponic CF meters is designed to show the strengths required for hydroponic growing. The scale ranges from 0 CF which is pure water, to 100 CF which is generally the maximum strength required. The scale, therefore, is divided into 100 parts, each part is a CF. unit.