Is this Fungus Gnats or a pH problem?

Well, the leaves are curling under at the leaf margins and 1 branch fan has started to brown and die off! At first I thought this could be caused by my tap water (don't use it ne more) being very high in pH like around 8.2. But I also have a slight (hopefully) fungus gnat problem. Here are some pics of the damage.
I ordered some "double death" predatory nematodes to kill the gnat larvae, and have switched to RO distilled water. Anything else I can do?

Anyone out there? Could use some insight please.

I dont really understand why u think its fungus gnats, u will see em if it is

I do see them on the surface of the soil. I have sticky traps and a lot get caught, but there are still larvae in the soil that are prob eating my roots! Would fungus gnats cause this if they ate the roots? Or is this indicative of a pH problem?