In true l'oreal advert style - here's the science bit! Blanketweed thrives in high-phosphate conditions. By avoiding phosphate inputs (fish food, tapwater) and introducing assimilative phosphate control you can starve it out.

In other words, only top up your pond with rainwater and introduce emergent plants which won't get smothered and will lock-up some nutrients. Watercress is the best one that I know, unless you fancy the tender floating plants such as water hyacinth which is used for sewage treatment in some tropical countries. You can grow the watercress that you buy in supermarkets - it'll root within a few days but will be more effective planted in a pond basket to ensure that it doesn't run out of nutrients such as iron. Keep it from flowering to encourage lots of hungry vegetative growth.

The only wildlife-friendly organism that eats it is the Ramshorn snail Planorbis. Other snails such as the Great pond snail Lymnaea will eat plants.

Adding native plants for shade will help - try Callitriche, Nuphar, Nymphoides or Nymphaea.

You can add phosphate-removing resins available from decent aquatic retailers and these work if you add enough relative to water volume. Barley straw works by giving off small quantities of hydrogen peroxide as it decomposes but it's a bit erratic..