Yellow stripes, crispy leaves.

Hi all, we have 2 plants under a 400w HPS.
They are being given Bio-Bloom nutes, in the correct doses.
The water is at around PH 5.5-6.5, 2 liters every 3 days.

It will be 30 days into flowering tomorrow, but over the last few days the leaves are beginning to get yellow 'burn' like stripes.
This is only on one plant specifically.

I hope the pictures attached will show what I am talking about, any information as to what can be done to prevent more of this would be much appreciated.

1st picture - the 2 plants.
2nd/3rd/4th pictures - the problem, yellowing.
5th picture - Lower fan leaf on the OTHER plant, strange discoloration??

Light burn

im no expert at all but i have heard stories that aluminum foil can burn your plants if it is reflecting to much light into one spot other than reflecting light evenly...

hope this helps...

I doubt that aluminum foil is reflective enough to really cause light burns, although it DOES contribute to overheating in general.

The fear of hot spots though is one of the reasons I prefer WHITE walls (paint or Panda) and even one of my MH lights has a white-enamelled reflector.