The question as asked, is not a safe one for anyone to answer. Bottom line, yes you can kill fish and plants with Hydrogen Peroxide if not done very carefully.
If the root cause of the algae (most likely low or fluctuating CO2
) if not fixed, it will always come back.
Seachem Excel will provide Carbon, and has a side effect of killing algae. IMO
, that is a better/safer way to go.