I have heard of the Tetra product, but have never used either one. I really can't speak for them because of that. In my tank I achieve blackwater through a combination of a lot of Malaysian driftwood that was never pre-soaked, a large mixture of Indian almond leaves and oak leaves, and occasionally I add some alder cones. Normally I would think it was carbon removing some (one reason I don't use it), but you already said you're not using chemical filtration. I'm also loathe to tell you to use more of those products because I don't know enough about that and if they have an impact on water quality such as possibly lowering the pH too much too quickly.
How often are you doing water changes? No tea coloring at all?
How often are you doing water changes? No tea coloring at all?
