Koi Pond Filtration: Skimmer + Bottom Drain vs. Winter Operation in NJ

Planning 12x18x3 ft koi pond (5 koi + others). Mixed advice: bottom "pressure filter" + skimmer/biofilter? Winter: run waterfall year-round or shut down? Fish hibernate Dec–Apr?

Filtration for Koi Ponds

• Bottom drain + skimmer → vortex → biofilter is modern standard for koi.
• If mixed species (frogs, plants), bottom drain may harm them.

Winter in NJ (Zone 6/7)

• Run waterfall 24/7 if depth ≥ 3 ft — moving water won't freeze deep.
• Shut down if shallow or risk of power loss/ice dams.
• Koi don't truly hibernate — metabolism slows but they need oxygen.
• Gas exchange critical — keep hole in ice (aerator/de-icer).

Decision Factors

Depth, power reliability, risk tolerance. See winterizing guide.