Yellowing of the lower leaves????

My plants are 21 days old....the bottom set of leaves is getting a bit yellowish on most of the 9 plants...im sure its some kind of deficiency, but since I fed them a week ago and got some major nute burns on some plants.....im wondering if I should feed again?

Pics to come....at work at the moment.

if they got nute burn i would let them go a week without nutes and then start again adding abit less and see how they respond.

Overnuted......give'em only water for a few days...and hope they're not nute-locked.

Yeah seems like the over nutes stunted em for a bit...i watered 3 times since and still..they look a bit slow going compared to before the nutes.
But the yellowing just showed...like last night....

try using a nute flusher if it becomes worse... but just water for now as you would do usually with no nutes