cbb asked: I have a 22×15x4(deep) koi pond with a liner it sits bellow ground, has a debris filter, marginal and several lillies. The pond has been established for two years now. The koi range from approximately 3 large (12 inch) 8 medium (5inch) 15 assorted from fry to 1.5 inch.
I also have a waterfall and am aware that UV filters also destroy beneficial bacteria.
Gabriel