with out a doubt, THE VERY BEST investment i've ever made has been buying the hanna combo meter, i have three, and yes i have OCD too.....my plants love me!
i'm using 4 scoops maxibloom to 5 gallons RO and calmag which gives me a PPM of 950 @ .5 EC conversion. depending on the strain i'll let the runoff get as high as 1100-1300PPM (depending) before i give them some water to bring them back down to around 8-900PPM. my vanilla and OG #18 kushes...