If the plant pond is higher then the fish you could setup the plumbing such
that you filter the water from the fish pond and pump it back into the plant
pond.
Let the plant pond overflow into the fish pond. Install a cutout in the
pipe from
the filter to the plant pond so that you can divert the water into the fish
pond
thus bypassing the plant pond. This would also allow you to use the plant
pond as a veggi filter to help out the fish.

Howard

"Don Lasko" wrote in message
...
Wanted to add another pond this Spring. Not sure if I want a 2" pipe that
can be closed to keep both waters separate or a 4 foot open connection
with
a bridge.

Pond 1 2800 gal. with koi. Pond 2 to be for plants about 800 gal.

Thought if I kept them separate, I could salt or medicate the koi area and
not hurt the plants.

Which configuration would be most practical?

Also, would I need to seam the two liners?