At first glance, plumbing a koi pond — a backyard body of water stocked with colorful fish — looks simple. You connect the pond, bottom drain(s), skimmer and filters together using pipes and pumps into a continuous closed loop system — just as you would a swimming pool.
Except, this isn’t a swimming pool: The need to gravity-feed water from the pond to its mechanical and biological (beneficial bacteria) filters, and then return it to the pond, requires an approach to piping that minimizes friction at all costs. This is why the best koi pond designers use wide-diameter (4-inch or larger)
