The only way the water will get dark brown is if you get the really dried brown oak leaves. Those are really hard to find right now this time of year.
The branches with the dried leaves I've brought home are just the ones I KNOW aren't contaminated by animals. There's so many dogs running through the parks just marking their territory. I hate going through the woods trying to avoid these foul organic mines.
I just notice OFL's post on the scientific research on the 2 sets of leaves. That's all I needed to see and that's good enough for me.
I've NEVER seen the black walnut tree on my walks, so I should be good.
Like I said, my fish never seemed stressed at all even when the leaves were covered in some cloudy white slime that formed on the edges on day 2.
I still have no idea if that white stuff on the leaves is normal though. Look at the leaves next to the cleaned out test tubes.