yea not that Bad at all, just your plant using up stored Nitrogen from the lower fan leaves as it don't have any left in the medium and you don't provide enough in your watering schedule, up the N a bit, but only a bit, remember your in the middle of flowering, now is actually the time to up the P and K and not so much the N
in the future, try to keep em nice and dark green up to this point, if you see em get pale green up the N a bit, then after week 4-6 you lower it a lot and maybe even cut it near the end
best of luck
Slip