i wouldnt give up on soil over some gnats, the best tasting and moset potent herbs are grown in soil with organics imho, i use molasses in every feeding too, but for gnats i do this, add the sns root drench every other feed, and surround the outside with home defense max, grow basil in the tent they also hate neem oil it also makes them retarded and forget to breed!
true story neem stinks like onions and body odor, but it screws with their brains the first time i got gnats from fox fof soil i sprayed neem oil in the top of the soil and all over the plants i witnessed them becoming retarded with things like trying to fly upside down ,forgetting to flap their wings and falling to the floor mid flight ,landing on the light and incinerating themselves, it was a frikkin evil comedy i laughed so hard ,i call neem oil "retarded bug in a bottle" its cheap and lasts a long time so give that a think, i am not thrilled with my dwc bucket hydro, keeping up with ph is annoying, you cant use all the really kick a$$ amendments, i tried using seaweed,azomite,dark matter, and it gunked up my system, another thing to consider is bugs are not attracted to really healthy plants in nature they go right past them to the less healthy or sick plants, this info has pushed me to try to get mine so healthy bugs dont want them, now im not saying that your plants are not healthy just sharing info, i hate to see a grower leave soil over something so fixable, hydro is cool and can grow some amazing plants, but i truly believe organic fed soil is the primo way to go,and is so much better for the environment
just sayin