[Ted L. Dutcher]

Interesting comments.
Peter mentioned “Oak Extract” well, I can tell you that my test bucket with Oak leaves is a lower pH than the test with Oak, driftwood and Indian Almond leaves, although the Oak has less tannin coloring. Unfortunately I did not test the driftwood and Almonds seperately. I suspect the driftwood (mopani wood)is highest in tannins but not in acidity.