We encourage our customers to prepare all of our aquatic botanicals before use- whether it's by boiling, soaking for an extended period of time- or a combination of both.
Let's face it- some aquarists like the concept of "blackwater." They just don't like the idea of having leaves, seed pods, cones, etc in their tanks.
A lot of hobbyists use leaves to brew a sort of "tea" with Catappa, Guava, and other leaves, by rinsing the leaves off, soaking them for a day or two in freshwater, then boiling them for about 15-20 minutes (about 6 large leaves in about a half gallon of water). They will let the "brew" cool off, discard (gasp!) the leaves, and pour the liquid through a coffee filter into a glass jar or food grade plastic container.
When you're ready to use the "tea", simply pour the desired amount into the aquarium. How much? Well. that's the million dollar question. In my experience, it takes a surprisingly large amount of this extract to lower the pH significantly in an aquarium, but this is dependent upon the hardness of your water. I have found that it's tougher to lower the pH significantly in hard water.
You can knock the pH of your tank water down with this type of extract, but there is no real "exact formula" to do so, in my experience. I'd experiment with some of the extract and a quantity (say a gallon) of your tank water in a bucket or other container (without fish, of course), and test the pH before, during, and after the additions. This will give you some idea as to how much of this extract to use.
Always proceed slowly when you're using this extract (or anything intended to alter your water chemistry, for that matter) with fishes or other animals. Slow, gradual, measured changes are far, far better than rapid, uncontrolled ones.
You'll be able to jude for yourself the effects of this technique, and enjoy "the tint" without actually having the botanical materials in your aquarium. Just another way to incorporate the benefits of tannins in our aquaria.
Go slow. Be careful.
And Stay Wet.