http://cannabis.com/growing/ph-what_is_a_good_ph_EC_tds_meter.html
http://cannabis.com/growing/ph-What_are_the_differences_between_ppm_and_EC.html
http://cannabis.com/growing/ph-ppm_ec_cf_chart.htmlv

All I have to say is make sure your watering solution (With and with out nutes) is properly pH'd before you apply.

Keep Smoking and Peace Out,
SMG