With an EC meter. It's the only practical way actually.
stinkyattic Reviewed by stinkyattic on . When to add nutes? Hey Everyone- I've got my seedlings in DWC under 400 MH and they seem to be doing great. Right now they have 2 sets of real leaves and looks like the 3rd is developing. When is the right time to start adding the nutes? Thanks. Rating: 5