Removal of Algae Using Hydrogen Peroxide
I use one pint of 3 percent hydrogen peroxide for every 1,000 gallons of water
Always measure out the hydrogen peroxide you put into your pond by using a measuring cup.
Pour the solution into the pond, make sure it is away from fish.
Allow the hydrogen peroxide solution to settle in the pond for a day.
After a day, use the skimmer or fine net to scoop out the grime and dark slime from the pond. For small amounts of algae, I use around 50 ml each day for 3 days which just degrades and passes through the filter as sludge.
Should you have any problems with the fish which is most unlikely just drain 20% of pond water and replace.