Quite often, even plants with 90%+ Indica genes get thinner leaves during flowering, so this is quite normal in my experience.
It is as though the plant "knows" that by getting thinner leaves during flowering, that it will help pollen get to the flowers, rather than have the flowers hidden under huge, wide, fat leaves.
Silica gel will do nothing, ventilation is the only real way of removing excess humidity easily and quickly.
I presume you are not running a humidifier, but if so, unplug it, your plants will be just fine without it, they really don't need any extra humidity at all, ever, they are not rain forest plants, but lowland dry season plants in the main.
You can still change to dark during the day, just give them an extra long day to change the timing, one extra long day will not upset them, especially now, while they are still in veg.
Hope this helps, Organoman.