yellowing during veg

hi ther folks i have been vegging for 6 weeks first attempt of lst all was going well untill a week ago some of the underneath leaves started to go yellow but i thought this was normal due to lack of light but a few days after that a few of the the top canope leaves started to turn yellow ph 6.9 78f lights on 65 lights off humidty 55 every 4 days just water then 1.4 ec ppm do use think i should flush in case of lockout of nutes thanks in advance peace

anyone any thoughts

If your still in veg, I'd think, by the sound of it, it's N def. What nutes are you useing (N-P-K-)? Feeding schedual? Soil/Hudro?

Really need some pix if possible. But without them, I'm sticking with N def.

i dunno it could be a nitrogen deficiency....PICS?

thanks for the replies guys having camera trouble just now will try again tommorow the yellowing is mostly on bottom leaves and slightly on top leaves growing in soil all in one mix feed with bio grow 1.4 ec then leave for 4 days then i just feed with clear water