The most common reasons for blanket weed are, excess nutrients in the water, clear water, and too much sun.
UV lights kill off the suspended algae cells which make the water green, but leave you with clear water. This in turn lets the sunlight penetrate the water and encourages the filamentous strains of blanket weed.
Possible solutions are chemicals(don't like them, but they work) but some of these will have an adverse effect on other plant life. Lots of lilly leaves on the surface(bit early for them yet). Or you could shade the pond on the sunny side to cut down on the amount of sunlight the pond gets in a day.
There is an electric blanket weed controller similar to what you put on your water system indoors to reduce scale in the pipes. I think it is called "The Weedmaster". A search on the web should find it. I can't say how efficient it is though. According to the makers it will solve your problems forever, but I have never been convinced.
Hope this helps.