not mold.
are you giving it full strength nutrients? if so, just give them 1/2 to 3/4 strength. better yet, go get a PPM meter and make sure it stays under 1200 for now (you need to calibrate the meter first!!!).
also, your PH is too high. keep it closer to 6 for soil and 5.7-5.8 for hydro.
could very well be nutrient burn. are any of the leaves cupping up from the center or the edges, i don't see any in your pictures. if they are, this could be stemming from a magnesium deficiency. but i would say nutrient burn.
questions:
-is this hydro or soil?
possible solutions:
-flush these bitches. 2gal of water/1gal of grow medium.
-back off on those nutrients and get a ppm meter to check it. they are a bit expensive if you're poor (like myself lol), but it's 100 bux. and you're talking about your babies here, they deserve the meter!
-PH 6 for soil and 5.7-5.8 for hydro, check on it as often as you can and keep it there.
could you post some pics that are focused on the leaf, not the mylar
also, try to post some of the whole plant as well.
im about 95% sure this is nutrient burn, since it started when you switched to flowering (switched nutrients), and i'm guessing your not checking the PPM of the solution since you haven't posted it. please post full plant pictures before you go flushing them though.