I don't know if this is a viable option or not but would it be possible to divert the water from the pipes coming into the pond down past the pond outlet on the other side of your fine mesh filter? This would allow mechanical removal of your invasive Australian Swamp Cropweed without sending plant fragments downstream and clogging up your fine mesh filter.

It sounds like you have a horrible invasive aquatic plant and not a lot of good options to deal with it.

https://www.cabi.org/projects/project/33138

Welcome to the forum.