Fertilizer injectors should be checked for accuracy on a regular basis. The following is a simple procedure to follow for checking your injector.
Procedure to check the EC of a fertilizer solution:
1) Let plain water (no fertilizer) run a little, then collect water in a clean bucket. Take a sample of the plain water from the bucket. Check the EC of the untreated water supply.
2)Mix up your fertilizer as you normally do and run it through the injector and hose. Let it run a little to be sure you get an accurate sample. Take a sample of the fertilizer-injected water from the end of the hose and use your meter or soil test laboratory to check the EC of the sample.
3) Subract the EC value of the untreated water from the EC value of the fertilizer water.
4) Compare the results to an EC chart from the fertilizer manufacturer or fertilizer bag. The chart will correlate the EC measurement with the ppm Nitrogen so you can determine if your injector and mixing procedure is accurate.
Information from the New England Greenhouse Update Website