1. I think your plants are being over watered, I just took a quick look at the pics didn't quite read through all the posts, but at a quick glance let them dry pretty well before watering, just water until you can see the water first trickling out of the bottom. Make sure its not to humid in the room and also you want a lot of light, with temps being below 77. This will help plants to dry out, make sure you have a shit ton of circulation and run co2 if you can. Make sure all your pots have enough holes on bottom add some if you have to you want the water to drain properly, don't back your soil too tight and don't use soil that is too dense, if you have to mix coco with fox farm.
2. with the gnat problem you want to use onyx all natural spider mite spray, this stuff does wonders, keeps your leaves green and healthy it has oils that are great for leaf shine. It stops powder mold and other molds. It also kills bugs and keeps them away. I use this throughout my grow spray a other week and never have bug or mold problems.