Blabbering on about bark...

If you've been following the goings-on here at Tannin Aquatics over the last few years, you've seen us consistently offer a variety of bark and bark-related products. Part of the reason, besides the desire to offer you the widest selection of natural materials for botanical-style, blackwater aquariums, is because we feel that bark is an excellent vehicle for imparting tint-producing tannins (and their associated humic substances) into your aquarium water.


Bark not only is functional, but it provides a very cool aesthetic touch that really represents nature in a realistic way. As we've talked about endlessly here over the years, branches, logs, and (by extension) tree bark and such combine with leaves and seed pods in natural waterways of the world, providing shelter, supplemental food, and environmental enrichment for fishes...and they do the same in the aquarium!

As a source of tannins, bark is significant. Tannins are naturally occurring plant polyphenols, and are ubiquitous in trees worldwide, in the leaves, roots, branches, and of course, the bark. Bark functions as a protective barrier for trees, and it provides a thick, waterproof covering to the living inner tissue. It protects the trunk against the elements, disease, animal attack and fire.

Tannin is typically concentrated in the inner bark (known as the "cambium layer") of trees. According to botanists, older trees have bark which contains  more tannins than a younger tree, and, consequently, the lower parts of a tree contain a higher concentration than the top parts.

And of course, some trees are more significant sources of tannins than others, among them The Cutch tree (Senegalia sp.), the Indain Almond Tree (Terminalia sp.), and members of the family Rhizophoraceae  (Mangroves!), all of which we "tinters" play with!

 Let's check 'em all out briefly.

Cutch Tree bark is interesting. It's used in it's native range of India and Southeast Asia variously as a food additive, astringent, tannin producer, and dye. The tannins within the bark are extracted by boiling the wood with water and utilizing the resulting "brew"- hmm...sounds just like a "blackwater extract" to me!  And of course, it has a unique aesthetic component which can really be utilized in interesting ways in the blackwater, botanical-style aquarium.

While I always discard the "brew" from boiling, I've used this bark for some time now as a means to impart that tint we love she much into the water, as well as for a unique aesthetic touch. And, most recently, as a substrate to breed bottom-spawning killifish- a perfect replacement for long fiber peat moss!


The Indian Almond Tree is almost legendary in our geeky little sector of the fish world, as it's leaves are sort of the "default" tannin-imparting vehicle for virtually everyone who plays with the blackwater aquarium. And the bark is equally as useful, but perhaps lesser utilized in the hobby. We're so obsessed with the stuff that we offer it from both India and Borneo- and each is slightly different in "format."  

The leaves (and the bark) are used in different herbal medicines in the tree's native range, and, as we've investigated before, the bark and leaves are known to contain agents which have been found to control and eliminate chloroquine (CQ)-resistant and CQ-sensitive strains of bacteria.

Anecdotally, the hobby has attached to this "feature" of Catappa, and all sorts of miraculous claims seem to be ascribed to the stuff! Indeed, research has shown that there are definite anti-fungal and anti-bacterial benefits for ornamental fishes when utilizing concentrated extracts of the compounds found in the leaves and bark; however, it's hard to determine the efficacy of the actual leaves themselves as a "tonic" of sorts. I prefer to think of them as a nice source of color-producing tannins and of humic substances, which have been known by science for some time to be highly beneficial for fishes.

And then we come to mangroves.

Now, while Mangrove bark is not something that has been available in the hobby, to our knowledge, we've been fortunate enough to find a source for legally-collected mangrove branches and roots from Hawaii. 

And with some experimentation, we've seen these branches (and leaves- but that's another story for another time!) impart a definite "tint" to the water of both freshwater and brackish aquariums.  Something worth experimenting with more, for sure! I've been using in in my latest blackwater aquarium, and I feel it has significant "tinting" properties, for sure!

So, bark in general is very interesting stuff, with a wide variety of functional and aesthetic benefits for aquaria. We can't vouch for the aquarium suitability of all sorts of bark, but we can certainly advocate the use of Catappa and Cutch Tree bark! Now, I have a hunch, but no specific data to back it up, other than superficial observations-yet it's a "hunch" that bark may have a greater concentration of tannins than leaves. I say this because, at least from a visual perspective, I've found that it takes far less in the way of bark to impart a similar visual tint to the water as it does leaves. Definitely something worth experimenting with over time!

Preparation of bark for aquarium use is pretty straightforward. You need to either soak it in freshwater for an extended period of time (several days) in order for it to saturate and perhaps release any surface contaminants (dirt, dust, etc.) that may be present, or boil the stuff in a pot for around 40 minutes or so, followed perhaps by an overnight soak in room temperature water. No worries- this stuff has enough of a "wallop" that this preparation won't "deplete" it of it's valuable tannins! If kept dry, it can be stored indefinitely without losing its effectiveness. This is verifiable if you talk to anyone in the tanning trade who utilizes bark for creating stains.

As a food source, well bark is interesting! I've seen some fishes (the usual suspects like Plecos) rasping at it, as well as some shrimp.

More interestingly, I've seen fishes such as characins (Pencilfishes, in particular) picking at the bark quite often! Now, it's hard to tell if they are picking at the bark itself (perhaps unlikely, as gut content analysis of the wild fishes mentions nothing about bark!), or more likely, at algal, fungal or other growth on the faceted surfaces of the bark. Nonetheless, bark can at least foster some of the natural food sources of a variety of fishes and shrimp, and is worth considering as a "functional" component of your blackwater aquarium.

And of course, you could simply use bark as you would leaves or cones- in a filter sock or perhaps (I have not personally tried this) i na reactor. And of course, you could throw a piece or two (you'll have to determine how much for yourself) into your water preparation/storage containers to "pre-tint" your tank water a bit.

And of course...the stuff just looks pretty cool!

In the end, we think that once you try bark, you'll end up as obsessed with it as we are, and consider it a vital functional and aesthetic opponent of your blackwater/botanical-style aquarium. Likely, over time, you'll come up with other uses for bark in your aquarium (perhaps as a substrate, spawning surface, or shelter for various fishes), and we'd love to hear about it!

Until next time...

Stay curious. Stay innovative. Stay experimental. Stay engaged. Stay tinted! 

And Stay Wet.


Scott Fellman

Tannin Aquatics

Scott Fellman
Scott Fellman


1 Response


February 20, 2018

I’ve had great success with bark in my aquaria as a long-term tinting agent, a “prep” botanical for upcoming water change replacement water, a building block for caves, and a great source of biofilm and algal growth. Yesterday I did a rescape on one of my tanks that had 1mm elm bark in it that was over a year old, and while it may have been a bit “flappy” it was still holding together!

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