Sin Sueño

Your instincts are right... she's showing early signs of a calcium deficiency which NORMALLY shows up due to pH issues - however, your pH is spot on. The other thing that can cause this is too much nitrogen which can lockout the calcium that is already being provided in your other nutes. If this was my grow, I would to two things: I would first decrease the amount of Bio-Grow by half and I would add 1 tsp calmag - but only use this once a week. Too much calcium will produce its own problems. Good luck with your grow - you've done a really nice job so far, especially with the SOG!