Ha ha Guest, if we knew that we'd patent it and get rich quick! ;)) Green algae is a fact of life in ponds. You could try a UV filter like I did, very expensive, no effect whatsoever (very disappointing). You could also try a straw block under the water....might help. It helps to not have trees overhanging or too much sunlight on the water, and fish seem to make the problem worse as they make a lot of much which adds nutrients to the water that the algae love. The only way to keep a balance is to have good filtration and one third of the water covered with oxygenators. Also, filling the pond with tap water is also supposed to make it worse (nutrients again) so best to fill it with rain water from your water butt. Hope that helps...it's not easy!

It will go now its winter and come back in Spring/summer when the sun comes out. I use barley straw, water lillies, oxygenating plants I planted a tree to give the pond shade and that works for me. I dont have a pump which is another way.

its an enzyme in the barley straw that stops the algae growing , we still get greenish water ( at least it hides the fish from the heron ) but no blanket or duckweed

I dont get them either Pamq, I dont mind the greenish water either and its getting clear in my pond now. The fish are still very evident as it continues mild here.

And they're the two main problems, tap water and fish. You need more plants/oxygenators to counteract the effects of the fish by-product (poo) to balance out the nutrient levels. Phil

I collect rain water for the pond and treat tap water if I am forced to add any in the draught like we had this year and I remove some plants and reduce the oxygenators in the autumn/winter Phil so I assume you next spring?