The transition- the approach, the process, the myths, the unknowns...and the art.

"I want to set up a Blackwater Aquarium."

Those words are impactful to me. And they're getting more and more common all the time. 

Okay, I sound sort of ridiculous, but I think the concept of blackwater aquariums is becoming sort of, well...trendy.

I guess it's cool.

I mean, it IS. But it's like we've tended to focus on the superficial aspects of it- you know, the cool looks. Awesome, but only really part of the story. Also, it's likely the the most superficial part. Again , it's okay to enjoy the "look", but I'm afraid that in the "insta-trend" thing, a lot of people are taken in by the color of the water, the aesthetics- and the perception that simply adding "botanicals" to the aquarium gives you soft, acidic "blackwater" conditions.

There's more to it than that.

Obviously, I'm giving myself a bit of a "pass" here by referring you to the "body of work" that we've developed over the years here...I mean, in one summary blog post, I can't give you the definitive guide to blackwater/botanical-style aquairums.

Yes, we've talked quite a bit about the processes involved in setting up a botanical-style, blackwater aquarium from scratch, as well as the mindset, research, concepts, and execution involved. More than could possibly be summarized in one concise blog post or article! It's literally taken about four years to sort of get out the basics about what we feel is a good approach to the blackwater/botanical-style aquarium game.

Yet, regularly, we hear from a large number of interested hobbyists, customers, and community members who have an existing aquarium and want to "switch it over" to a blackwater aquarium. We receive a fair number of questions about the process, so I figured that now is as good a time as any to touch on it!

Now, I've always had this "thing" about most aquarium-related "how-to" type articles, because I think they tend to offer up information as if everything were simply a "recipe", and that if you "do this" or add "a bit of that"- you're certain to achieve "such-and-such" a result... I always feel that this is a bit of a "broad stroke"; one that sometimes glosses over the more nuanced aspects of the topic.

And you know as well as I do that, with hundreds of possible variables in the equation, an aquarium is no "picnic." Nothing is a "given", even when you're considering trying to hit a narrow range of conditions with seemingly "the right" combination of actions. And our idea of throwing in leaves, twigs, botanical materials, and soils into a tank and seeing what happens is about as "variable-inducing" as it gets!

So, with that "disclaimer" in mind (LOL), we're going to at least look at the overall "how to", and we can all fill in the blank spaces in our specific situations with more customized approaches as needed. The purpose of this piece is not to give you the definitive answer to "How to create a blackwater aquarium" or whatever.

There's so much more to it than a superficial piece like this could ever hope to offer. We're just giving you some "highlights" here, and hoping that you'll take advantage of what's available. You'll have to do additional homework with resources available here in previous blogs, and in articles and blogs throughout the internet and elsewhere. 

No real "shortcuts" here.

"OMG Fellman, just get to it already!"

It starts with some basic questions.

First off, the obvious questions we need to ask ourselves when commencing such a change are, "Do the fishes which I keep come from this type of environment in Nature?" and "Am I willing to take the time to do it slowly?" The answer to the first question is pretty obvious- and it's almost sort of insulting that I'd even mention it...but "due diligence", ya' know...

Okay, you got that one.

The second question is to me- more fact, it's, as we say here in America- "The whole ball game.." (they probably say that in every country, too, but hey...).

Patience. Observation. Time.

Essential "ingredients" in the botanical-style blackwater aquarium game.

One fact:

It goes without saying that, if you've been keeping your fishes (even ones which come from blackwater conditions in Nature) in harder, more alkaline water, there will need to be a gradual transition to this type of environment. It goes without saying that rapid environmental changes are potentially harmful to many fishes. 

Now, in the bigger picture, I am of the opinion that even, for example, Tetras or other fishes that may have been bred commercially in "tap water" conditions (not necessarily soft and acidic) for the past few decades still could benefit from being "repatriated" into more natural conditions.

However, you're still putting them through an environmental change, and this requires time.

Where do you begin? 

Well, you start by seeing where you are. "Getting your bearings", so to speak.

I'd start by doing a sort of "baseline assessment" of the pH and alkalinity of my water. Digital meters are a great investment that will make accurate monitoring of your water very easy and economical. You should also give some thought about what your target pH/alkalnity are. If you're using tap water with a pH of 8.2 and considerable carbonate hardness, for example, you need to consider how you might bring these measurements down.

And you should, in my opinion, be willing to make the "infrastructure investment" (pricy though it may be) in a reverse osmosis/dioinization unit...or at least, finding a source of good, consistent RO/DI water (many fish stores will sell you RO/DI by the gallon/litre!). The rationale here is that it's far, far easier to reduce the pH in water with little or no carbonate's more "malleable"- a better "canvas" upon which to work.

If you aren't using RO/DI water in your current setup, you can even start gradually mixing some in (without adjusting it or adding anything) with your regular water exchanges. Arguably, this may help to gradually lower the carbonate hardness and pH. Yet, it's going to take a long time. Ultimately, the idea is to replace all of the water in the tank with RO/DI. Patience is essential. Slow steps. If you can get your water to around neutral (7.0), that's a great "stepping off point" for modifications to lower pH levels.

Oh, there are other considerations- like substrate. If you're using a substrate which has considerable "buffering" capability, than it's likely that you'll either need to replace it, or accept the fact that you will likely not achieve "soft, acidic" conditions.

Now, speaking of pH- I wouldn't "shoot for the stars" and try to get to 5.5 or something really low right out of the blocks. For that matter, I wouldn't obsess over ANY specific "target number", really...Rather, I'd try to find a tight range that you could easily maintain. With the understanding that you need to do this over a period of weeks- even months...I'd shoot for a modest pH level of like 6.7-6.5 as your target range...Get a feel or operating a tank under these conditions and maintaining them consistently. 

Once you've got a sort of "handle" on the pH and alkalinity, and have gotten them "in range", you can begin the (slow) process of "fine tuning" your habitat. Now, you might be (as I often am) surprised to find that botanicals and leaves, while impactful somewhat on pH, will drop levels much more slowly, and to a lesser extent than you might think. And if you have harder, alkaline water, the impact will be even more minimal or even undetectable.

As we've mentioned many times, the impact on carbonate hardness from botanicals and leaves is essentially nothing. They won't accomplish "softening" of water- a myth that's been erroneously ascribed to them for decades. A study of basic water chemistry will bury this myth once and for all. 

You simply need to utilize other methods to reduce KH (like the aforementioned use of RO/DI water) before even starting to add the botanicals and leaves, if your goal is to reduce pH in the system with them.

The other, probably insultingly obvious thing to be aware of is that, even if the water looks dark brown, it's not necessarily 6.3 and zero KH. I mean, tannins will stain water in the absence of chemical filtration media to remove them. They may not significantly impact the pH, as mentioned above, but you'll get that "visual tint." 

And I know many hobbyists who are perfectly happy with that.

And let's talk about the idea of tannins and humic substances for a second. We know that they are released into the water as a result of steeping botanical materials. And yes, there are commercial test kits to measure tannin levels (usually used in winemaking and such). They will give mg/l readings, which are, unfortunately, of no real use to hobbyists at the present time.


Because we simply don't have baseline information which hobbyists can interpret about tannin levels and/or humic substances in natural habitats, nor an analysis of which of the hundreds and hundreds of tannins and humic substances are typically found in most blackwater habitats.

At this time, we simply have to go with the understanding that these compounds ARE found in natural blackwater aquatic habitats at varying concentrations and combinations. Until further research is completed, interpreted and analyzed, we unfortunately simply have to "trust" this stuff! Yet another reason to study the wild aquatic habitats of the world even more closely.

I am also not aware of any studies done on the health impact to tropical fishes of tannins and humic substances in harder, alkaline environments versus soft, acidic ones, so it's sort of an open topic, really. 

Not exactly 100% definitive, completely confidence-building stuff, right? I mean, we know that these things are there. We know they're important, but we don't know a whole lot more at this point- at least, not hobby-wise. 

We're still at the phase when what we do is much more of an "art" as it is a "science." Now, that's not a bad thing, mind you. Just something we need to take into account as we peruse our work.

Speaking of the "art" part, let's just touch on the practical applications of botanicals for a second.

My personal tendency is to start with relatively small quantities of materials, usually leaves, and then work in the more durable botanicals like seed pods and such. I guess my thought process is that materials such as leaves tend to break down more quickly, imparting their humic acids and tannins into the water at a corresponding pace.

And of course, after your initial additions, you should measure pH again, to see if there has been any impact. A lot of hobbyists are into checking TDS as well...We've beaten up that subject quite a bit in past blogs here, and it's discussed a lot by hobbyists, so it's something you might want to research. 

Obviously, the question here is "how much stuff do I start with?" And of course, my answer is...I have no idea. Yeah, what a shocker, right? I realize that's the least satisfying, possibly least helpful answer I could give to this question. Or is it? I mean, taking into account all of the possible variables, ranging from the type of water your starting with, to what kind of substrate material you're using, it would be a shot in the dark, at best.

My advice is to start with conservatively small quantities of, maybe a half a dozen leaves for every 15 US gallons (56.78L) of water. You might not even notice any difference..or you might see a .2 reduction in pH...You have to test.

I recommend a digital pH meter for best accuracy.

I would make it a habit to add the same amount of materials (leaves initially, and pods if you want to mix 'em in on subsequent additions) at a regular interval. Say, every 4 or 5 days. Test again. See where you're at. I would tend to shoot for not reducing your pH by more than .5 per week. That's me of course...your fishes' tolerance and your personal comfort level with doing so is your call. And it's really a matter of repeating this process until you hit your desired range.

Notice I said "range" and not "target pH" or whatever?

We receive a lot of questions about utilizing chemical filtration media while using botanicals, and again, there is no "right or wrong" here. I will tell you from my personal experience that I like to use filtration materials like Seachem "Renew", small amounts of activated carbon ("Seriously, Fellman? Activated carbon?" Yes, really.), and Poly Filter on a full-time basis in my systems.

The reality is that organic scavenger resins, carbons, and materials like "Renew" might be indiscriminate in their removal of stuff like humic substances, tannins, and other organic compounds released by the botanicals, but they also tend to moderate things you don't want, like ammonia and "miscellaneous" organics (how's that for a "cop out" on my part...falling back on "generics!").

We toss a lot of  botanical materials (ie; "bioload") into our aquairums, all of which break down and require a bacterial population to "process" it. Why not have some chemical filtration as an "insurance policy" to remove some potential excess organics and such which will place a substantial burden on the bacterial population?

Yeah, they might remove some of the visual tint, but they will remove a lot less of it if you don't use the recommended "dose" per gallon. And frankly, I've never done a serious test to see exactly how much of what various chemical filtration media actually remove from the water. Being honest here...I'll bet not too many of you have, either, right?

So, we're kind of relying on the manufacturer's instructions and good old observation. Don't worry about the "tint" these materials will remove if used in moderation. Trust me, the water in most of my tanks is pretty damn dark, despite full-time utilization of these media! 

If you're getting a sort of feeling that this is hardly a scientific, highly-choreographed, one-size-fits-all're totally right. It's really a matter of (as the great hobbyist/author John Tullock once wrote) "Test and tweak." In other words, see what the hell is going on before making adjustments. Logical and time-tested aquarium procedure for ANY type of tank! 

Now, the interesting thing that I've always found with my botanical-style, blackwater aquariums is that they tend to find their own "equilibrium" of sorts- a stable "operating range" that, once you find yourself doing the same procedures (i.e.; regular, consistent water exchanges, additions of botanicals, and media replacement, etc.) at regular intervals, tends to remain highly consistent as long as you keep them up.

I've talked repeatedly about the (IMHO mostly unwarranted) fears people have about precipitous pH "drops" and "crashes" and such, and I believe that most or all of these things are mitigated by consistency, patience, taking small steps, testing regularly, documenting and repeating them.

I've said it before an I will repeat it once again: I believe that pretty much every one of the "anomalous" pH "crashes"/disasters I've heard of in regards to blackwater, botanical-style tanks has been directly attributable to "operator error"- i.e.; failing to be consistent, diligent, and conservative. Tanks simply don't "crash" by themselves, in my experience.

They fail as a result of something we did or did not do: Failure to slow down. Failure to measure. Failure to observe or continue to follow procedures that have been giving us consistently good results. In my experience, tanks will typically show "signs", develop trends, and demonstrate the manifestations of "issues" gradually...if you're attuned to them.

Botanical-style blackwater aquariums are not "set and forget" systems, exactly like reef aquariums, planted "high tech" tanks, Mbuna systems, Discus tanks, etc. You need to observe and "pivot" as situations dictate. A sort of "yin and yang", if you will, between pushing the limits and playing it safe... And you have to ask yourself if this type of "active tank management" lifestyle is for you! 

Failure to move thoughtfully, slowly, and deliberately, testing and tweaking along the way, along with time-tested, common sense application of aquarium management technique can result in you killing every fish in your aquarium. 

That's reality.

So, don't be stupid or lazy and you'll be fine.

Now, within the "Things are awesome!" range and "Oh shit!" range, there is a ton of room for experimentation and research.

"Best practices" in terms of how much stuff to add, when to add it- when (or if) to remove it, etc. are still the subject of much discussion among members of our community, and are evolving daily. There are, as we mentioned before- no specific "recipes" to follow...only those emerging "best practices" developed by those of us who have ventured along this path.

We can tell you about the benefits, show you how to prepare botanicals, advise you about husbandry, and warn you of the things that can go wrong. The rest is up to us as individual hobbyists.

And that's not only the challenge- but (in my opinion) the appeal- of this aquarium specialty. We all have an opportunity to contribute to the state of the art. To increase our body of knowledge of how these systems operate. To unlock the manifold benefits- and potential pitfalls- of botanical-style aquarium "practice."

It's not for everyone. Not everyone likes the look. Not everyone likes the work and effort required. And the lack of a "recipe" or complete certainty. There are still many "unknowns" and no single way to achieve "success."

However, for those who choose to walk on this most interesting path- the potential rewards for us- and most important- for our fishes- are huge.

And really exciting.

I guess this article may not have answered all of your questions..In fact, it probably opened up quite a few more, spurring you to do more research before starting a blackwater, botanical-style aquarium...That's never a bad thing!

Stay excited. Stay conservative. Stay experimental. Stay diligent. Stay skeptical. Stay hopeful. Stay creative. Stay curious ..

And Stay Wet.

Scott Fellman

Tannin Aquatics 






Scott Fellman
Scott Fellman


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