You have to be very careful doing this. Gnats are usually from the soil. Keeping the soil a tad too wet makes it a bit worse.
Sticky traps, spray neem oil on the soil and leaves and a bowl of apple cider vinegar inside the tent. The little buggars will fly right into the bowl and drowned trying to get at it!
A potato quartered length wise and laid face down on the soil will also help draw the larvae out of the soil. Put two in baggie in the fridge and put two on top of the soil and throw out after about a week and use other two. It will take 2-4 treatments to get rid of them.
Yes, they have no roots so they are getting all their water thru the leaves. Thats why they need pH water sprayed and domes over to keep the humidity high!