@KJLive - an alternative method of using H2O2 is sodium per carbonate. It's a powder that you can sprinkle on damp rocks that, once in contact with water, breaks down into hydrogen peroxide and soda ash. Great stuff - easy to use, relatively cheap and works like a charm for cleaning waterfall rocks. If you've ever seen the commercial products like EcoBlast or Greenclean sold for ponds, that's exactly what they are - in pretty packaging at an expensive premium. I also use it in the spring, similar to a product MicrobeLift sells that you sprinkle on the pond and all the organic debris from the bottom magically rises to the surface to be skimmed.
We buy sodium percarbonate in 40 or 50 lb buckets about once every three or four years. The price ranges a bit from year to year - this last time I pay about $2 a pound. In the past I've found it for as low as $1 a pound - just have to shop around and be ready to buy when you find it. It's sold as an additive for laundry soap mainly, for people who like to make their own soap. But you'll find reviews from people who use it to clean green algae off of roofs, siding, patios, or boats.
By contrast, EcoBlast on Amazon is currently selling for $8 a lb in the 7 lb package or $14 a pound in the 2 lb container. Same exact product inside the container. As a new pond owner I bought the stuff and thought "this is a great product but wow - too expensive!" That's when I started researching what was in the product. I think this link will take you directly to the SDS for EcoBlast:
Aquascape EcoBlast™ Contact Granular Algaecide eliminates unsightly algae and debris from waterfalls, fountains, streams, and rocks on contact.
www.aquascapeinc.com
Just to be clear - I have no issue with any pond product manufacturers selling this for a higher price. They have costs associated with sourcing and packaging and labeling and shipping, etc. And some people may only need 2 lbs once every couple of years and be happy paying that price and not having to store the product. We happen to have multiple water features that get green from time to time and for us, purchasing this way makes more sense!