Get yourself a PPM and PH meter. Mix the nutes at 1/4 the recommended strength and check the PPM and PH.
PH should be around 6.5-7.0 (you have a larger range of tolerance with soil)
Myself, I prefer 6.8.
Your PPM will vary with strain and plant size.
However, I feel a safe starting PMM is 300-600. If you are later in flowering, then you can give them more.
The best thing to do is feed, then wait to see how they react. If they like it, increase the dosage SLIGHTLY (about 100-150PPM) and again, wait to see how you react.
The best advice I have ever heard anyone give (and I hear it reiterated throughout this site) is:
LISTEN TO YOUR PLANTS. THEY WILL TELL YOU IF YOU ARE DOING SOMETHING WRONG!
(problem is, sometimes you need an interpreter to figure out what is wrong, heh!)
jE