pretty sure thats a never

You can use hydrogen pyroxide but I forget the ratio. Is your pond new? If the water is green you have to be patient and it will go away. Even quicker is you add lots of plants that cover about 75% (or more) of the surface to block the light and compete with the algae. A UV light will also clear green water (single cell algae), but not other kinds of algae.

Algae growing on the sides of the pond is good. Floating, bubbling algae not good.

Give it time. I has this notion that people fuss more about their ponds in the beginning - I know I did. Once it settles in you will find you don't have any issues of great note if you keep your plant count high and your fish load low, and have good filtration/circulation.

When we first fill our ponds we are in wonder of the clarity and then..... oh no - the green. But, it's a pond, not a fountain. It will clear in time if you stop playing with the water chemistry and get lots of plants instead.

I have not emptied my pond since I built it in 2003 and the plants are big and fill much of it. The water is clear. I do top off and do small partial water changes 2 or 3 times per year. Keep dead plant material out and vac the bottom out once or twice a year to get the junk you miss. Keep the leaves out if you have overhead trees.

Peroxyde works on string algae, but I've never heard whether or not it works on pea soup algae. Since your pond is small, I'm assuming you do not have a skimmer. If you did, I'd recommend quilt batting to strain out the algae, but in your case you might try erecting some sort of shade cover over it. Algae must have sun or bright light.

I agree with the above, but I've added the dose for peroxide from the forum's FAQ below.

Even with my small ponds H2O2 hasn't worked for me. String algae I remove by swirling a toilet brush to manually remove it. And suspended algae - green water - quilt batting around my submerged pumps (changed or rinsed frequently for a couple weeks), then... yes, lots of plants for 75% surface coverage.

I have a 300ga, a 175ga, and a 150ga ponds. Simple DYI skippy type filters. I just use some quilt batting around the pumps in early spring before the plants get going.

As CT says... best of all is patience :)

Good luck! S

Here is a link that might be useful: How do I do about green water?

Hydrogen Peroxide 3% per volume, only works to kill filamentous algae, i.e. string algae, blanket algae, angel-hair algae.
It will not help with "green water," caused by suspended single cell algae. Commonly known as "New Pond Syndrome".

Patience is a must, even though you find it frustrating and do not do water changes, as that only starts up the "green water" process all over again.
Allowing your pond to mature, with lots of bare rooted plants, to use up the nutrients in the water, will eventually help the water to clear.
Try water lettuce, water hyacinths, true watercress, or even bare rooted impatiens, stuck in between rocks,into the water. They are all hungry plants that suck up the algae feeding nutrients in a new pond and starve out the suspended single cell algae.
As Nancy said, filtering the water through polyester quilt batting removes the algae and can help speed up the clearing of the water.
"Horton"

Horton is correct. Also if you can find a fellow ponder in your area that has a pond that is at least five years old and can get about 30 gallons of that pond water and add it to your pond your pond will clear up in a couple of days or less.
Mike

Getting water from some one else's pond is also a great way to bring in parasites and viruses. I'd just wait it out. The pond will cycle and clear on it's own, assuming the fish are not being over fed and the filtration is adquate for the load on it.

Plants are essential, UV light will help - patience is the "winner", once the system is balanced all's well. NOTHING HAPPENS QUICKLY IN THE POND.