is your HPS light on for the pics? Looks orange. Turn lights off and use your camera flash. Makes for much better pictures to look at for us lurkers.
For the gnats I was going to suggest a layer of play sand on top of your medium but it looks like you are top watering so that might not work well. Another option is get mosquito dunks. Brake a small piece off and put it in whatever bucket you use for mixing up your feed water and always leave that chunk in the bucket all time with feed water. They say it lasts 30 days so replace after that. That way your watering will kill the gnats. Dunks work great on gnats. Maybe water very well if a dunk based solution and then a quarter inch of sand on top after that and let it sit for a day or two. That will kill em.