I'm also one week in, and have the gnats. They just come with soil growing. I got them with every brand I've tried.
I've heard this from so many people and it's honestly what deterred me from soil growing in the first place. I'm not one to back down from a challenge though so this will be a fun learning experience. Plus I will say its extremely nice not having to water 1-2x a day everyday like in coco.