i don't think it's nute burn as it is only showing on the bottom of the plant. this indicates that it is a mobile element problem. since it's a mobile elelemnt, it moves to where it's needed so you don't see the deficiency in the new growth.

how long have they been in their current pots?


-shake
headshake Reviewed by headshake on . Nute burn? Pictures/troubleshoot included What is your experience level? NOVICE Your Equipment: .1) Type and wattage of lights. T-5 .2) Distance from tops? 2 IN .3) Reflector type? T-5 SET UP .4) Is there a consistent fresh air supply? NOT AS MUCH AS ID LIKE...CLOSET GROW FOR VEG .5) Do you have an exhaust fan and a circulation fan? NO EXHAUST, YES CIRCULATING FAN .6) What are the bulb wattages, kelvin ratings, and schedule? UNSURE Rating: 5