"The carbon conundrum"

As the practice of blackwater/botnanical-style aquariums evolves and gains more and more traction, we seem to question some off our old habits, develop new ones, and dismiss some of 'em altogether.

An example?

We receive a lot of questions about our opinion on using activated carbon in blackwater aquariums. Now, for decades, carbon has been like THE premier form of chemical filtration for all sorts of aquarium application. As you might imagine, if used properly, carbon excels at removing dissolved organic compounds, certain "impurities", and...gasp- tannins from the water.

Now note the "used properly" part.

It's pretty well known that carbon is not a "set and forget" filter media. It's a chemical adsorbent media. That means that "stuff" adheres to it's surface. You use it to remove whatever it is your trying to remove, and replace it regularly..Like every two or three (if you're um, lazy...) weeks. Being an "adsorbent", stuff will adhere too it's surface, rendering it essentially useless very quickly as a chemical filtration media...at some point, it's just accumulating biofilms and becoming a biological filtration media.

My bias towards using carbon in my aquariums comes from years of keeping reef aquariums, and later, co-owning a commercial coral importation/propagation facility, which had thousands and thousand of corals in tens of thousands of gallons of water. Corals produce copious amounts of slime, mucous, and metabolic waste, not to mention "allopathic compounds" (ie; chemical "weaponry" used to defend their turf against intruders) and carbon,, along with admittedly more efficient means, such as ozone and protein skimming, formed a sort of defensive "triad" to keep the animals healthy.

Oh, and water exchanges, of course.

And yeah, we used a "shit ton" of the stuff in our facility! 

For reefers, the benefits of carbon use are really pretty apparent:

It reduces discolorations in the water.

It may bind some organic toxins.

It can be a place for beneficial bacteria to use as a "culture media."

It may remove copper and other trace metals (which bind to organic matter which, in turn binds to activated carbon for removal.

What about for us- the "BWBS" aquarium crowd?

I'll often tell people that I use it more-or-less "full time" in my blackwater, botanical style displays, and this elicits the online equivalent of raised eyebrows now and again. "Tinters" will ask, incredulously, "Doesn't this stuff remove the color from the water?" To which I respond, "Yes, it does...to some extent."

Please do look at some pics of my tanks, and tell me if I've been removing "too much" tint!

The key to keeping your tank "tinted", as we've mentioned before, is to continuously replenish the materials you use to tint your water (leaves, etc.). So, now one could probably make some sort of argument that using the carbon the way I do is actually sort of inefficient...Especially if I'm replenishing the botanicals as fast as the carbon removes them, then changing out the carbon. Yeah, I'm keeping the manufacturers happy, I suppose!  


I mean, is the stuff really even doing anything when employed this way? Just sort of playing "tug-of-war" with the tannins? I say sheepishly, "Likely." Carbon is perfect for a "prefilter" in reverse osmosis units, removing impurities to protect the delicate membranes that do the magic. That's like the ultimate "best" aquatic use for carbon, if you ask me. 

However, it also removes various dissolved organic compounds, which tend to enter our aquariums when we toss in- ohh- I don't know- leaves, seed pods, wood, etc.  Stuff like that. An access of these organics could have some long term impact on water quality, leading to algal growth and accumulation of nitrate over time. So carbon sort of acts like a very first line of defense against the accumulation of these compounds.

We've heard the occasional story over the years of the hobbyist who dumped his/her entire "Enigma Pack" into an established 20 gallon tank at one time, creating- well, "issues" with water quality. While not being able to remove everything you throw at it, carbon "in situ" could at least be helpful in removing excesses in emergency situations until you can execute a water exchange.

I employ a relatively small amount of the stuff (like about 4 ounces/114 grams) in an area of my filter where significant water flows through it. When I use carbon, I change out the stuff every two weeks without fail. One other argument against carbon is that it will remove medications from the water. Well, yeah- and that's important in a "hospital tank", dedicated solely to treating your fishes. However, if you're medicating your display tank, particularly with the intent of being "prophylactic" I personally feel that it opens up other important questions...like why you're not doing this in a quarantine tank and medicating the display tank instead! 

That being said, carbon- like any filtration media, or piece of equipment, should never be used as a replacement for common sense husbandry- specifically, regular weekly water exchanges. In fact, personally, I'd rather more people ditch the use of carbon and simply rely on water exchanges to remove dissolved organics and other undesirable compounds, from their aquarium water.

Alternatively, I tend to use other chemical media, such as "Poly Filter", which is really my "go to" for pretty much every aquarium I keep. Again, a lot of my personal practices are based on habits formed over a lifetime of personal and professional aquarium keeping, and some of them, quite frankly, are not the best way to go. Some might even be a bit...well, inefficient.

Old habits sort of die hard with me. However, the idea of creating some sort of emergency safety net for water issues is appealing to me, having seen a lot of "situations" over the years. 

It just makes me feel better.  Perhaps it's simply a quirk of mine. So, what's the answer to the question: To use, or NOT to use carbon in YOUR blackwater/botanical-style aquarium? 

Well, if it's used correctly, replaced frequently, and you understand what it can and cannot do, I see it as a sort of "insurance policy" for your aquarium. On the other hand, a well-managed aquarium in which common-sense husbandry is practiced (careful stocking, feeding, water exchange, etc.) doesn't really "need" it, IMHO, and you should simply have some on hand for emergencies.

Sure, this is a question with supporters on both sides of the fence, and both positions are justifiable. At the end of the day, carbon is just another one of those things every hobbyist should have a basic understanding of, and keep in his/her aquarium "toolkit."

What's YOUR take on this?

Stay diligent. Stay curious. Stay observant. Stay cautious...

And Stay Wet.


Scott Fellman

Tannin Aquatics 




Scott Fellman
Scott Fellman


Leave a comment