I personally mixed 1/4 cup H2O2 and 1 cup brewed chammomile tea into a quart of water and used it to spray the surface of the soil and the seedlings. Never got damping off and the seedlings didn't seem to mind it one bit.
I've always used a 10% solution of (3%)H2O2 for seed soaking ie. 10ml of 3% H2O2 in 100ml of water. camomile can be very effective for preventing dampening off