tanins ar ok with me they won't harm my fish because my water is so hard i would need a 20 foot baldcypress to lower the ph, the koi colors i prefer are the darker colored so it will hinder the viewing quality but it would be sweet to have a tree in my pond. the pond is already tanin heavy due to squirrels shredding acorns into the pond, solved that by cleaning it out of acorns and putting a fine mesh net over it, koi and goldfish and channel seem to be fine with the tea water.