Very pleased to report - fixed!
It was just that one rmangy/rusty knot, but I learned quite a few things from you here before being able to sort that out. Also connected the line back to itself in a full loop, and now I have nice strong current all the way along the line.
Thank you so much for your inputsuggestions and help with this - you TASers are just so brilliant!
Will use your additional suggestions when I attempt to install the extra loop to close off the hay area next
(hope I won't need any more consulting