Your plants use a LOT of nitrogen to produce strong roots... Thats why clones always turn yellow when they are rooting.. its a Nitrogen Deficiency.. If i were you I would clip off the bottom couple leaves that are yellowed.. and up the Nitrogen slightly in your feed.. Getting rid of the yellow leaves will alow the plant to heal.. and stop trying to repair dead leaves.. Those leaves will never turn green again.. so you may as well get them out of there asap! Good luck dude!