They still might yellow in the next week or so. Keep an eye on them. Your water level looked fine from the other thread. Keep the water level just below the surface.
If you are getting mold then you are not letting enough air get to the plants. I'd keep the top open a little more. Especially since you are in Hawaii, where its pretty humid already. It's more important to keep the plants wet right at the beginning, because the roots are not there yet.
The mold will go away when you fill the tank, so don't stress too much.
That HC is going to grow much faster than the hairgrass.