Mangel und stress?

btw, your EC value may be perfect, but overall concentration is not the only concern... each individual nute is relavant. ratio and concnetration of your fertilizer must be in line to work effectively

red stems can be low S. red petioles are a sign of low P -- 2 distinct symptoms with different causes. This assumes pH is fine and your overall EC of mix is good too -- they both seem okay from pictures. what products you use to get there is mostly irrelevent. these products are made of ubiquitous commodities, so don't overpay for fertilizer. sometimes it is just genetics. Also, intense led will bring it out, if isolated or more pronounced at top. lack of Mg does not cause red stems. it takes 4-6 weeks from the time a mg deficiency starts until the time you see symptoms. it causes interveinal chlorosis and spots. you can google image search any leaf symptom chart and it will verify this. i don't see a whole lot of yellow. leaves could be a bit more lush with no problem. if it's moving up the plant and tip-in progression, then it's N. if it's interveinal t hen it can be numerous things and i'd wait until it becomes obvious before reacting. great thing about slow moving issues is that you are close to being spot on and only need a small adjustment.

Red stems can be magnesium deficiency, but is also common to see streaks in stems when they stretch for flowering. As far as the rest goes it looks like it wants a little more potassium. I would also check your run off ph. It may be drifting out of a preferred range, and your catching it early. 👍🏻

Add pk booster or more bloom nutrients.

EC and pH value is perfect