1. Residue from nutrients
2. Infestation; Fertilized egg sacks laid by "your guess is as good as mine." If so, I suggest using a cotton swab (Q-tip), clean and warm soapy water.
Dip the swab in the warm soapy water, then while holding the leaf carefully but firmly, wipe the area. A Seinfeld moment - NO DOUBLE DIPPING. Enough said on the point.
3. pH Fluctuation; scroll down... http://weedfarmer.com/cannabis/plant_abuse_guide.php I use the entire website as one of my references. Good to have as a Favorite Bookmark.
Ref. Gorilla Grow... Be mindful that this plant could grow to 3 meters in height, as is the case with most outdoor Sativas.
It'll probably require some type of support system as well, a trellis perhaps?
Happy tropical trails...

