[Wu]

The best way to reduce blanket weed is to:

1 - Decrease the amount of nutrients in the water.

2 - Increase the amount of the surface which is covered.

The most elegant way of doing this is to bung in more higher order plants (water lillies, for example). They eat the nutrients and grow over the surface, so solving the problem in one neat stroke.

Just don't make my mistake and use duckweed. Although it worked a treat, it has now become a nuisance in its own right !