An excellent way I'd making sure your plants receive adequate water is to wait until you see drainage at the bottom of the pot, then in an hour or two, water it a second time until you see drainage. This ensures adequate/even watering, and helps eliminate dry pockets.
Gnat off and a forte fumer(bomb) got rid of mines after trying several different methods.....I also have the DIagard powder ....but......felt this would have to be a last resort if I used it.......let us no how you get on with it.........I have anouther bomb on standby just in case.......kills the flying one's stone dead then the gnat off takes care of the larvea......but make sure you use it for at least 2weeks........