interveinal chlorosis with spots -- increase Mg.
looks like a soilless/hydro type setup, so 75ppm Mg is a good target to hit. Compare that to what you have provided the last 30-40 days and it will help verify the answer if you gave significantly less than that. Mg symptoms take 30+ days to be visible on the plant from the start of the problem. you really do need to look back as far as 30+ days to be certain of it.
other variables are relevant. This assume ratio of nutes are not whacky, otherwise, and not constantly changed playing mad scientist :P