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?