Help Needed - experienced growers only please

[doctor_chronic]

Hi there,

I'm having some problems with my widow clones.
I'm fairly experienced and have been using ebb & flow for about 4 years.

Ebb & Flow System. SOG style 18 x widow clones
Flood every 15 mins from 1 hour (fine)
Expanded Clay
Nutes - Canna Veg & flores
Supplenting with Canna Rhizotonic at 4 ml per litre
Nute Temp 76F
EC 1.4 - Tap water at .6 so actual nutrient level only at .8
Ph - 5.6 to 5.8
Light - 1000W Son agro 2 feet above canopy

Clones in day 9 of veg - Only just started to exhibit symptoms.
Turning them soon and need to fix this ASAP

Only older lower leaves twisting and curling - turning brown NOT FROM TIPS rather all over leaf. - NO YELLOWING

General growth is rapid with these clones at 10 inches in day 9.

Feels like a ph / nutes issue but after calibration and retesting - this is good at a range of 5.6 to 5.8 throughout a 24 hour day.

Roots CLEAN & WHITE

Resembles light burn BUT NOT on top of canopy.

Same system, same clones, same nutes I have always run without trouble

Any experienced growers got some advice?