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I see recommendations talking about E.C, CF and pap. What are they and what is the difference between them?

In hydroponics, they are all measurements of the dissolved salts in your nutrient solution. These measurements include all salts, whether fertilizer salts or non-nutrient salts already in the water such as common salt. These salts are commonly referred to as the 'background conductivity' of your water and can be measured using a conductivity meter.

E.C stands for Electrical Conductivity, CF stands for Conductivity factor and pap stands for Parts per Million.

For reference, 1.0 unit E.C equals 10 Cf units which approx. 725ppm.

As different chemical salts produce different conductivities, the conversation for your grow room will depend on the actual combination which varies from chemical to chemical. The table below is representative and is accurate enough to be used effectively.

What conductivity levels should I maintain for my grow room?

This depends on the growing method, environment, strain, climate and nutrient. Here are some general guidelines.

Vegetative: E.C 1.6 - 2.2
Cf 16 - 22
Ppm 1150 - 1600
Flowering: E.C 1.8 - 2.4
Cf 18 - 24
Ppm 1300 - 1750

You should follow the instructions on the hydroponic product label. However, if you keep to the middle of these ranges you shouldn't go far wrong. With a bit more experience you can experiment and come up with what suits your situation best.

What will happen if my conductivity is too high for my grow room?

Your plants growth will slow down and if the conductivity is way too high the edges of the leaves will start to burn. Your plants will lose production because the plants will try to conserve water by reducing their growth rate in order to survive. In serious cases of over fertilizing, you will eventually burn the roots and the plants could die. If the conductivity is raised suddenly to a high level from a much lower one then water can be drawn from the plant roots leading to severe root damage.

What will happen if the E.C is too low in my grow room?

The plants will be pale and stretched. They will starve and quality of the produce will be poor. If you drop the conductivity suddenly from a much higher level to a low level you can damage the roots and stems of the plants as water pressure in the plant increases.

What is a conductivity meter and do I really need to use one for my grow room?

This is an accurate electronic measuring tool for measuring the electrical conductivity of a solution. It works by applying a voltage between two or more electrodes submersed in the solution. The meter then monitors how much current is passing between the electrodes as a gauge of how many ions are in the solution. Be aware that meters may give readings in E.C, Cf or ppm and some meters may give readings in E.C, C.f. or ppm and some meters may do all three. You really should use a conductivity meter to make up your nutrient solution. It is possible to grow without using one but it is more of a hit and miss affair.