-- yup, some Ca-Mg is wise when using RO/Di water,.. this will help stabilize pH in solution as well, just make sure the Ca-Mg you use has carbonate in it, as this is the ion that's directly involved with ph buffering in solution,... because RO/Di, or any really low ppm water has very little to no CaCO3 in it, the buffering is gone... this makes it prone to wild pH swings from even small inputs,... (don't bother trying to take a pH of such water, the meters get confused of sorts, because of how they work).... Always add the Ca-Mg first, and let it sit after stirring well for a few minutes to react some,.. then add nutes, and adjust pH if needed,...
That said, I'm not sure I see any symptoms of Mg defc., or that I can tell in the pics at least,.. 3rd pic with the funky leaf formation, it looks like a flash reflection, or is it actually paled out like that?
....the color on the petioles is more likely normal expression, especially in a BB strain,... true, P defc., sometime K too, can cause this, but it's not a reliable symptom alone because of this,... :smoking: