looks like a magnesium lockout from either a buildup of nutrients in the soil or your soil ph is out of range. check your runoff water to see what your problem is. if the ppm/ec goes up dramatically then continue to flush because you have buildup. if the ph is out of range then flush with the opposite end of the range until it balances out.
Looking good. You look to be 1 week ahead of where I am and I have had the same issues as you and pretty much using the nutes. I wonder if bio bizz is just too light for them or takes too long to amend to the soil.