h2o2 isn't too stable in the presence of light, it quickly bereakes down to H2O and H2.
i take the plant out and sit on the concrete, i fiull the syringe with H2O2 and squirt it onto the base of the plant (the BGA is always on the gravel on the surface of the pot) and let it sit for bout 30sec then dump it back into the tank. H2O2 also seems to kill snail eggs, or atleast stop them from sticking.