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...
Cannabis476 Reviewed by Cannabis476 on . 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. Rating: 5