Testing your fertilizer with EC meter 

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How to use a soluble salt-meter, or EC meter, to determine the level of fertilizer you're applying to your crop, In other words, to check your fertilizer injector.
In the greenhouse and nursery industry, most of the mineral nutrients come from water soluble fertilizers. It is very important to know the actual injection ratio and if the injector is working properly. If the injector is not working properly, it is highly likely that nutrient deficiencies or toxicities will occur.
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