A bunch of years ago I read that stuff doubles it's mass every 3.6
days. You need to keep on top of the removal process. Nets work.
Syphoning off the surface, along with the duckweed works. Surface
agitation does work (was mentioned by other poster).

The key is persistance. I had it in my tropical tanks and it took about
3 or 4 weeks.

But it provides some shade, it's a great nutrient sink for the pond
helping to keep it clean, and it's great natural food for the goldfish.
Why get rid of all of it?

Lilly