If you don't have an EC meter, just use what's on the label, but you really should have some way of checking conductivity if you are in a position to need calmag, and you'll want to add it until your ppm reads right around 300, before adding any other nutes or checking the pH.
stinkyattic Reviewed by stinkyattic on . If you use RO or distilled water you NEED CalMag Plus That's all. My fingers were cramping from typing it n times a day. Rating: 5