You think they look burned?
I really don't think this is the case because I thought when you burn them, you literally get burning to the leaves and major discolouration and death.

These plants are green and generally healthy as they are growing and thickening at a staggering rate.

The PH is around 5.5 and I use a 3 part brand name (Advanced Hydroponics) and follow the directions on the label which per 100 litres of water is 60ml/30ml/30ml for vegative growth at full strength.