i woud raise your water level,browning of the roots is one of 2 things rot or nutrient stains. deff bring the water level back up to the bottom of the pots,u wont hurt anything.hell thats how i veg cuttings,just a tub of water with vitamine b1 and superthrive.they sit there for about 2 weeks.as long as u have oxygen u wont have a problem.cannazyme will help like some one else sed,it eats old bad roots and causes benneficial bacteria to be released.how far away are your lights.my guess is your lights are 2 far away to really stimulate growth and 2 having the added stress of just trying to stay hydrated.so give it a shot for about a week .put those flouros about an inch or 2 from the top and raise the water level i bet u will see major growth in that time,deff 2/3 inches and much more root mass.if u want to stabalize your rez temps u can buy a seedling heat mat and put it under your bucket,or go to petsmart and buy aquarium heater with a temp controll for like 10 bucks.