by the Urban Gardener

Australia's online hydroponics supplies & indoor grow shop

WHAT IS THE BEST WAY TO CALIBRATE A TDS OR EC METER?

Most often gardeners use standard reference solutions. Their bottles have marking referring the conductivity value (EC), which is expressed in micro Siemens/cm, and the corresponding parts per million (ppm) values for such elements as potassium chloride (KCl) and sodium chloride (NaCl). Sometimes they also have a “442” reference mixture as well. Most often the standard of “1000-ppm NaCl” is used to calibrate the meter for hydroponic solutions, because NaCl (sodium chloride) conductivity resembles closely that of the hydroponic nutrients. It is necessary to follow the instructions provided with the meter to correctly make the measurements.

WHAT DOES A TDS OR EC METER MEASURE?

The meter applies an electrical voltage to the nutrient solution, causing the motion of mineral ions, which results in the electrical conductivity of the nutrient. Half of the conductivity value of NaCl solution (in microSiemens/cm) is close in numbers to its ppm value; therefore, the meters show the conductivity of sodium chloride as the equivalent of its amount.  

WHAT DOES THE TERM PARTS PER MILLION (PPM) MEAN?

This term is used to denote the concentration of various elements in the nutrient solution. One ppm is defined as one part of the mineral in one million parts of the solution.

HOW DO I CONVERT BETWEEN TDS AND EC READINGS?

To get the TDS value of sodium chloride, multiply the obtained EC figures by 1000 and divide by 2. To define the EC value, multiply the ppm figures by 2 and divide by 1000.

Let us suggest that EC is 1:

1x1000/2= 500 ppm.

In case if ppm is 500:

500x2/1000= 1 EC

IS IT BETTER TO USE AN EC OR A TDS METER?

A gardener may choose either a TDS calibration or an EC meter, depending on the recommendations to the plant nutrient: whether they are in ppm values or in EC units.

USING THE 3-2-1 FLORA SERIES MIXTURE, APPROXIMATELY WHAT TDS OR EC READINGS SHOULD I EXPECT?

Nutrient            EC (micro Siemens/cm) TDS meter (NaCl standard)

3:2:1                      2.3-2.5                       1350-1450

2:2:2                      2.2-2.4                       1300-1400

1:2:3                      2.1-2.3                       1250-1350

WHY IS CONDUCTIVITY OF THE NUTRIENT IMPORTANT?

Defining the conductivity of the nutrient solution, a gardener thus understands its strength, which matters much for the plants. The solution is stronger if there are many or too many dissolved solids in it. Tender or young plants roots may be burned with too strong fertilizer, which conductivity is very high. On the other hand, many mature plants require stronger solutions to improve the growth or fruiting rates. The strength can be increased by adding the concentrated nutrient.   

HOW DOES CONDUCTIVITY AFFECT PLANT GROWTH?

The plants can grow slower if they do not receive the necessary amount of the nutrients. If the conductivity of the solution is too low, the plants will “starve” and obtain too little fertilizer. Thus, higher conductivity will mean that the solution is stronger and contains more food for the plants. However, too strong solutions may harm the plants and burn their roots.

WHAT ABOUT FRESH AIR?

Proper ventilation and changing of the air improves the absorption of the nutrients by the plants. The matter is that they absorb nutrients when water molecules evaporate through the leaves. This is enhanced by the ventilation. Thus, there is definitely a connection between ventilation and fertilizing your plants and proper ventilation should always be maintained.