Help !! Urgent help needed

hi there, first time grower, having immense trouble, i showed pics to a few peeps, some say nitro def some say magnesium def,

small plants are white rhino, and the ones with the all over yellow are ak47

sitting in 25litres of ph'd 6.0 water on EC 2.4 using flairform green grow.
timer for 15mins every 2 hrs. water is not hard at start, doesnt even register on the meter,

sitting under 2 x 600 reds,

im absolutely stumped and really need to know what im doing wrong - please help asap

thanking u all

15 mins every two hours my be your problem

What are you feeding them? and what is the npk of the food?

What are you feeding them? and what is the npk?
Lighting schedule? Flower or veg