After looking at the pics i do not believe it is overfeeding in that sense. However you may have a salt buildup from all the feeding, try taking 3 times as much water as you have soil and flush it through. When you water are you just doing it according to a pre-set schedule no matter what or are you waiting for the pots to become light again? as for eliminating things 1. Your temps are absolutely fine, if you were in the lower to mid 90's and dont have good ventilation it might be enough to do some damage. but your completely safe.
2. Did you check your soil ph or is that number that the ph of the water going in is? a ph of 6.5 is right where you want to be, anywhere between 6.0 and 7.0 is acceptable, preferbly more in the middle, i ph my water to between 6.4-6.7 myself.
3. It's not the light being too close, light burned leaves have a totally different look from any of what your plants showing.