OP, did the tips darken first followed by the yellowing, or was it yellowing followed by dying leaves(dark tips)?
The tips darkened first, with a thin strip of yellow around that as it progressed.
To me, I don't know whats going on aside from the plant is stressed. I'd cut the additives and stick to the A/B. The look of the plants and the burnt tips make me think SOMETHING is not settling well with the plants "stomach". Check that you ppm meter is accurate and check your root system for any issues.
Changed my res with fresh RO and a fresh round of nutes, without the calmag and the rapidstart. Taking those two out of the equation should make this much less of a headache. I ended up making 50 gallons of RO, and added 20 tsp of both A and B.
I got some very sound advice from someone who, for lack of a better way to word it, knows his shit. It confirmed my suspicions of a P deficiency. Evidently my Sensi grow is pretty low on phosphorus, with the a being 3-0-0 and the b being 2-2-5. It was suggested I should pick up FF tiger bloom and use it in conjunction with part a, instead of b.
But for now, I upped my nute concentration, and am currently sitting at 184 ppm. I figure until I can get something to isolate the problem and take care of it, the added nutes should at least slow down or halt the deficiencies progressing. One could hope, at least...
Does anyone have any quick remedies for a P deficiency?