Assistance needed

hey guys, first time hydroponic (RDWC) grower here.

-My pH is at a constant 5.8
-Water temperature stays around 69-71c
-Grow tent Temps stay at 78c
-Grow tent RH is 55%
-PPM is 800
-SF4000 at 100% 26" from canopy
-using AN with calmag
-For Reservoir top ups I use de-chlorinated, aerated tap water
- 6" circular air stones in each bucket providing plenty of oxygen for roots
-The roots above water level are slightly brown and the submerged roots are nice and white

Can anyone please tell me Why they think my leaves are turning lighter colors in areas.

Thank you in advanced!

what size bucket you useing?

5 gallon buckets

Magnesium

Thanks guys!