I hate when it goes hydrophobic
had it happen before even watering every day. Wetting agent will definitely help. I've used dish soap in a pinch and it works but wouldn't use regularly.
As far as fungus gnats go, I don't have issues with them since I started using mosquito dunks. Like
@Fermented_Fruitz said, if you can find the bits it's easy to just mix with the soil. I can never find the bits so I just use the donuts.
I soak a couple in my water overnight and use that for the first watering of the soil, that way its active as soon as they start to hatch. If you use drippers you can stick a donut under the drippers for continuous hands off protection