Bark, like a dog. Tint like a geek.

People ask us what the fastest way to get a lot of tint into their aquarium is, and I have the most simple answer.


Yeah, bark.

Now, bark is interesting to me, because not only does it have an interesting aesthetic, in terms of it's "form factor"- it is a part of the tree which seems to have a lot of tannins and humic substances. In fact, the argument could be made that bark  has a greater concentration of these compounds than any other parts of the tree it comes from, because of the role of bark.

Tannins in the bark help precipitate out the enzymes and other protein exudates from bacteria and fungi thus not allowing these organisms to infect the tree. Tannin is typically concentrated in the inner bark (like, right below the surface), in what botanists call the "cambium layer." It is thought that older trees have bark which contains more tannins than younger trees, and by this measure, the lower parts of the tree contain a greater concentration of tannins than the top parts of the tree.

And of course, bark is known to contain agents which have been found in studies to control and eliminate chloroquine (CQ)-resistant and CQ-sensitive strains of bacteria. So, slightly more than anecdotal evidence exists that leaves and bark of many trees (Catappa comes to mind here) do have anti-fungal and anti-bacterial benefits for ornamental fishes when concentrated extracts of these substances are utilized in aquariums.

Of course, it's awful hard to determine the efficacy of the actual bark itself as a "tonic" of sorts, despite hobby-level claims. I prefer to think of them as a nice color-producing, humic substance-emmitting natural material which may have collateral benefits for our fishes! 

And of course, like many of the items we work with here at Tannin, we offer a few different varieties of bark. And interestingly, each brings its own unique aesthetic to the aquarium. Now, we'd be reaching if we suggested that each variety has some specific tannin or humic substance "profile"- although I suppose it's possible- just like coffee beans or wine grapes reflect the " terroir" (environment in which a particular wine or coffee is produced, including factors like the soil, topography, and climate) from which they come...But we have no real way of confirming that.

Suffice it to say, each type of bark we offer bring it's own "coolness" (technical term) to your aquarium!

We offer Catappa bark, the popular and sentimental fave, in several varieties from different locales. We offer Indian Catappa Bark, from Tamil Nadu region, which has a distinct rough surface area and comes in a rolled form factor. It has a very cool, almost "log-like" aesthetic.

Our other popular variety of Catappa bark is from Selatan, in Borneo. It is a "chunkier", thicker "cut", which tends to last almost indefinitely, releasing significant  color to the water, and recruiting biofilms on its hard surfaces. It's optimal for grazing fishes and shrimps.

The final "player" in our "trio" of Catappa bark is the variety from Sandakan in Borneo. It comes to us in a thinner, rolled "strip-like" form factor, making it perhaps the most "delicate" of the varieties that we offer; while still lasting almost indefinitely following submersion. It can be torn into smaller little pieces, supplementing more "ephemeral" materials like leaves on the substrate of your aquarium.

A lot of you wanted something that is truly "log-like" in both appearance and "scale", the recently-released Sri Lanka Mahogany bark is a fantastic botanical material for both creating a unique aesthetic in your hardscape, and for imparting a significant burst of tannins into the aquarium. Sourced from Kotugoda, Sri Lanka, this material is collected, rolled into sizable "logs", and dried. One thing about these bark pieces is that, although they have a unique shape that many fishes can exploit as a "shelter", we are not presenting them as a "Pleco Cave" or whatever. By happenstance, some pieces have wider openings, but it's purely random.

The latest, and perhaps most unique bark that we offer is Red Mangrove bark.  This bark comes to us from Hawaii, where it is legally collected and prepared for aquarium use. As it turns out, the Red mangrove is invasive in Hawaii, and the local government  and USDA are all too happy for us to take this material off of their hands!  We've used it for some time in aquairums, and I can tell you that it's  texturally interesting, aesthetically beautiful, and packed with tint-producing tannins! 

Yeah, it's neat to have we'll keep sourcing unique, sustainably-sourced bark for aquarium use. Wait- "sustainable?" Yeah, with the exception of the Mangrove bark, our suppliers collect their bark from their own, plantation-grown trees, which they rely on for other uses, like harvesting the leaves for aquarium use or tea.

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. The idea of either approach is to "crack off" the surface pollutants (dust, dirt, etc.) and to help saturate and sink the bark.

Now, a lot of people tell us they're concerned about boiling or soaking their bark pieces before using in the aquarium. Doesn't this deplete much of the beneficial tannins and humic substances that you want so badly? The answer is, in short- no.  You needn't worry- Trust us, this stuff has enough of a "wallop"of the aforementioned substances that any preparation procedures won't "deplete" it of its 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, the idea of using 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.

There are a number of ways that you can utilize bark in your aquariums. You could use it as a "filter media" of sorts, placing it in a filter or sump, where water will flow over it, passively imparting tannins, humic substances, and that lovely golden-brown color that we seek so earnestly.

If you've been considering bark in one form or another in your aquarium, we hope that this little "tour" of the selection, aesthetics, and "functional applications" of this botanical material can bring amazing benefits to your aquarium and its residents! 

Tint like a geek!

Stay informed. Stay excited. Stay curious. Stay creative. Stay persistent....

And Stay Wet.


Scott Fellman

Tannin Aquatics 


Scott Fellman
Scott Fellman


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