ahh i cant be bothered reading all those replies

but to clarify some things i have seen:
mussels wont help stringy algae, pea soup algae maybe.
UV clarifiers only work for pea soup algae, not stringy algae.
do not add more aquatic plants, they will steal nutrients from your terrestrial plants, they are better at soaking up nutes than terrestrial plants.
a cover will help, but dont be fooled into thinking that is a be all and end all like people here make out, i find that algae grows the fastest in my ponds in winter rather than summer.
DLF's advice is pretty much spot on.
Mussels and UV lights only work while it is at the microscopic level, not pasta.
Algae needs light to photosynthesize. No light, it should stop growing. This is almost impossible to do.
And of course you have more algae in the winter. Cold water holds more DO then warm water does.