help needed. yellow tops. pics

I am getting pale yellow(almost white in some cases) at the very tops of my flowers. the flowers below seem fine. hears some details of my grow.

ph 6.0(root zone)
EC 2.4
temps light cycle 28C @ cannopy
dark cycle 18C
root zone 21C
lighting 2 600w hps in cooltube
nutrient canna coco a/b
medium canna coco
additives hygrozyme
feeding 4.0 litres a day(10% waste)

She is rather tall as I don't really know how to do this yet(She just took of when turned to 12/12). could that be a factor? any way here is a pics.

sounds normal look at my pics

do u mean like that

i would say to much water and nutes

yea it could be too much nutes if there gettin a lil white

o did not see tha pic

yea looks like a nute prob

too much? I just raised the EC from 1.4 to 2.4 because being 6ft tall I thought it may be a defficiency of some sort. the rest of the plant is lush and the flowers on different lower branches are fine. I am running 10% waste and flushing once a week with water(0.2 EC) so I don't think salt build up is an issue. Should I go to 2litres a day perhaps?