Basil like neutral soil, maybe slightly acidic. Coffee grounds might be too acidic. if you use them use only a light covering on top of the soil, and bottom water if at all possible for a week or two until the gnats are gone.
I can’t give much advice since, while I have a green thumb, basil and cilantro are my kryptonite. Happens almost every year lately. Just can’t get them to grow, while my other stuff, dozens of types of veggies and flowers, are growing insanely well.
