Yeah, you can use carbon!

Like so many things we work with in botanical-style aquariums, the idea of using chemical filtration media seems to simultaneously make sense, while also seeming kind of counter-productive! That's a bit confusing! 

I guess you have to think of it in the context of what we do, right?

Brown water and lots of leaves and botanicals seems like perfect recipe for either a really natural-looking aquarium, or a simple disaster...depending upon how you look at it!

As the practice of blackwater/botanical-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. Techniques, ideas, and concepts start playing out and falling into place.

We receive a lot of questions about our opinion on using activated carbon in blackwater aquariums. Like, a LOT.

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. That seems kind of counter-productive...

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 that you're trying to remove, and then you replace it regularly..Like every two or three (if you're um, lazy...) weeks. Being an "adsorbent", stuff will adhere to it's surface, rendering it essentially useless very quickly as a chemical filtration some point, it's just accumulating biofilms and becoming a biological filtration media.

Personally, I love the stuff, and rarely, if ever have ran an aquarium without it.

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 and water quality high.

Oh, and we also employed 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 Blackwater/Botanical-Style aquarium crowd?

As we've discussed many times here, there is a sort of obsession those in our world have about keeping the water in our tanks dark and earthy-looking, and the idea of using chemical media with known adsorbent capability like carbon seems a bit "counter intuitive" to some. Carbon does excel at removal of compounds like phenols and tannins.

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 some extent."

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

The key to keeping your tank "tinted", as we've mentioned before, regardless of wether or not you use carbon is to continuously replenish the materials you use to tint your water (leaves, etc.). Think about botanicals as "consumables", in that they need to be replaced on a regular basis to maintain the characteristics you want in your aquarium.

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 the effects they impart, then changing out the carbon. Yeah, I'm keeping the manufacturers happy, I suppose!  

However, my real "secret" is to use less than the manufacturer's recommended dose. I use about half of what is typically recommended. Thus, I will still get some of the benefits (ie; removal of excess organics), while still keeping that tint which I love so much.

I suppose one could question my approach.

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 performs a number of functions when it comes to water purification. Not all of them are immediately apparent. Yet, the benefits of carbon use are manifold. For example, 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. (And don't get me started about RO/DI until. Suffice it to say, if you're into this kind of aquarium, you should invest in one. Period. Full stop.)

Yes, carbon excels at a number of things.

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 excess of these organics could have some long-term impact on water quality, leading to algal growth and/or accumulation of nitrate over time. So carbon sort of acts like a very "first line of defense" against the accumulation of these compounds.

And yeah, we'll hear the occasional story of the hobbyist who dumped his/her entire "Enigma Pack" into an established 20-gallon tank at one time, despite our instructions not to, 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 like that until you can execute a water exchange.

Of course, it's not a "cure-all", but carbon can help in these types of scenarios.  

It should be noted that activated carbon does not remove all possible toxins or unwanted chemicals, including the ammonia produced by animals, and nor does it substantially affect carbonate hardness of the water. Other compounds that activated carbon has little or no ability to remove include stuff like calcium, carbon dioxide, fluoride,  magnesium, nitrate, nitrite, phosphates, sodium, and iron.

Of course, it's important to use carbon correctly. Carbon should be placed after the mechanical filtration media in the filter, where water will flow through it with little restriction. Otherwise, the stuff will clog with debris and other solids, significantly reducing its available surface area for chemical adsorption. Make sense? Oh, and in these scenarios, activated carbon does recruit biofilms and their constituent bacteria, becoming a sort of biological filter. So, although this could be seen as a sort of collateral benefit, if you let your carbon sit too long, in a strange twist of irony, the sudden removal of portions of the natural biological filtration could actually be counter-productive-cause a sudden decrease in water quality!


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 it does- 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 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, especially if it encourages more diligent husbandry over just developing a "dependency" on a product.

All that being said, carbon and other chemical filtration media have their place, when used responsibly and as part of a comprehensive regimen of aquarium husbandry.

Alternatively, I use other chemical media, such as "Poly Filter", which is really my "go to" for pretty much every aquarium I keep. I also love the carbon "alternative", Seachem "Renew", which works very well. Yet another promising filter media is SeaChem's "Hyper Sorb", a synthetic synthetic adsorbent which, according to SeaChem's own "FAQ's" indicates that it's their "go-to" for use in blackwater aquariums! I love everything they make, so if the experts at SeaChem are giving Hyoer Sorb their blessing for blackwater, who am I to doubt it?

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 for everyone.

Some might even be a bit...well, inefficient.

Old habits sort of die hard with me, I admit!

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. Utilizing carbon or other media works for me.

It just makes me feel better.  Yeah, that's hardly a scientifically-supported, perfectly "technical" reason to do something in the aquarium hobby, but hey, no one ever accused me of being 100% logical, so...

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, frequent water exchanges, etc.) doesn't really "need" it, IMHO, yet 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 perfectly justifiable. At the end of the day, IMHO, using carbon is just another one of those things every hobbyist should at least have a basic understanding of, and keep in his/her aquarium "toolkit."

I've always felt it better to have than "have not."

But I am a bit weird, as you already know.

Stay observant. Stay curious. Stay prepared. Stay proactive. Stay curious. Stay diligent. Stay informed...

And Stay Wet.


Scott Fellman

Tannin Aquatics 



Scott Fellman
Scott Fellman


Leave a comment