T wrote:

I'm adding an additional filter to my pond. I have a 3 foot gap between it
and the pond and am contemplating various ways of spanning the distance. A
rubber lined rock course might be an option. I really don't like the thought
of PVC pipe. I was thinking about making a trough using corrugated
galvanized metal - that stuff that's so popular on the roofs of barns and
tool sheds. Does anyone know if GALVANIZED metal is fish safe?

It isn't. It is coated in zinc, which is toxic.

Try schedule 80 (dark gray) PVC instead of 40 (white) or DWC which is
green. Cut a real large diameter in half.

Otherwise, go see if you can find some clay tiles, like they use for
roofs, but you invert them so water runs in a stream.