Are oak tree leaves bad for the health of koi?
Question I have a small backyard pond with koi and goldfish. It is under a large live oak tree. I have heard it said that oak tree leaves are bad for the health of the koi but no one has said why. Besides the build up of leaves in the pond bottom (which I know affects water quality) what is it about oak trees in particular that is bad for the fish? I would appreciate any help you could give me on this. Answer Oak leaves, blossoms, and acorns contain various amounts of tannins and phenols which are toxic to koi (and other animals in varying degrees). The toxicity varies between species (red oak, white oak, etc.) and also from season to season. If you are able to minimize the amount of leaves, acorns, and blossoms that end up in the pond, there may be little impact on the fish. It may be more practical to move the fish (or pond) to a more suitable location.
