Just moved into a new house with koi carps, unfortunately there seems to be a very large problem with blanket weed. After trying an expensive treatment and also using the barley treatment, this does not seem to help.
At the moment we are using large canes to twist the blanket weed out of the pond, however if somebody has an easier way or come across something that actually works, please feel free to enlighten me.
I used the Cloverleaf blanketweed eliminator on my koi pond. It's about �12 to treat 3,000 gallons i think and is a white powder which you sprinkle on the water surface and allow it to sink.
It turned my water milky for a week or two but boy did it kill the blanket weed.