So I'm wondering what nute concentration I should be using right now? I assume very weak, but how weak?

AN recommends 15-30mL of MEST Grow per gallon. Right now I have 2.5mL per gallon.

I have half strength Humboldt Roots and Roots Organics Trinity Catalyst.

Should I put more MEST Grow in? I ask this because All but 2 of my plants have darker/reddish stems. I read this can be Nitrogen or Magnesium deficiency....