Planted Tank Guru
Join Date: Jul 2010
Location: British Columbia, Canada
If you only have plants in your tank, a "pond day" probably wouldn't hurt anything.
With fish, your filter should run 24/7/365.
Ponds without filters, are large volumes of water, with large surface area, and most fishes kept in ponds are hardier, like goldfish, that can normally withstand a less clean environment and lesser water quality than most other tropicals.