Just a quick note on H2O2. Hydrogen peroxide will kill the bacteria (good and bad) in the res. If you are growing with an already healthy res, it is a very bad idea to add Hydrogen Peroxide to increase oxygen levels.

When my plants are young I also submerge the bottom of the net pots. This guarantees the roots of the young plants are reaching the water. As Opie said, just bring the water level down as the roots grow out of the pot.