There are as many approaches to setting up aquarium as there are aquarists. Sure, there are a few "best practices" and such which you could pretty much count on, and then there are some new approaches and steps you can take, based upon our collective newer experience, which is changing daily.

We talk quite a bit about the process of setting up a botanical-style, blackwater aquarium from scratch, and the mindset, research, concepts, and execution involved. However, we have a large number of 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...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.

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.

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...

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...).

You must employ patience. You have to take the time. There is simply nothing to be gained by rushing this process.

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. Although fishes are quite adaptable, significant environmental changes are tough on fishes, and they need to be made slowly.

We've talked about it before, but I am also 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. I don't believe that a few dozen generations of captive breeding could erase the genetic adaptations that these fishes have made through evolution over eons.

That being said, and the lofty goal of replicating "natural conditions" aside, however, you're still putting your fishes from a stable situation through an environmental change, and this requires time. It's something that needs to be done carefully and thoughtfully, over several weeks, IMHO.

I suppose the most fundamental, absurdly obvious question is, do you want to lower the pH of the water, and if so, why?And, is this a good idea? Is it something that you feel will benefit your fishes?

Yes, seemingly dumb questions, but when you're embarking on a paradigm-shifting environmental change to an existing tank, and all of its inhabitants, it's important to give this a lot of thought. If you're just doing it to be part of the (fictitious) "Sub 6.5pH Club", or to humble brag on Instagram, or do a video on Tik Tok about your "cool soft, acidic water "or whatever- you need to reassess things.

Once you've been able to address that fundamental issue, the next steps are perhaps the most important ones.

I'd start the conversion process by doing a sort of "baseline assessment" of the pH and alkalinity of my water. I'd make sure that I have sufficient filtration in place to accommodate some additional bioload (you know, decomposing leaves and such). 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.

If you're using a substrate which is known to buffer the water, it's going to make the process of lowering the pH significantly an extremely challenging, if not nearly impossible, process. You may consider a total substrate switch- another process which can add extreme stress and biological challenges to your system. It's literally a "go/no go" item, IMHO. It may simply necessitate breaking down the tank completely and starting over...


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 hardness...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. This will help to gradually lower the carbonate hardness and pH. 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.

Now, speaking of pH- I know it's an obsession of lots of hobbyists... SO, here's the deal: 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-months, even...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 as I've mentioned many times over the years, if you have harder, alkaline water, the impact will be even more minimal. And the impact on carbonate hardness from botanicals is essentially nothing, in my experience. You simply need to utilize other methods to reduce KH (like the aforementioned use of RO/DI water).

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. Hard, alkaline tinted water is aesthetically beautiful, and the benefits of humic substances imparted by botanical materials may still be realized.

I am 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. Perhaps one that you could make meaningful observations about!

When "transitioning" an existing aquarium, my tendency is to initially 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 and carbonate hardness 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, so it's something you might want to research.

In addition, the more rapid decomposition of the leaves fosters more biological activity (ie; beneficial bacteria, fungal growths, etc.)

The botanical-style aquarium is a microcosm which depends upon botanical materials to impact the environment.

This microcosm consists of a myriad of life format all levels and all sizes, ranging from our fishes, to small crustaceans, worms, and countless microorganisms. These little guys, the bacteria and Paramecium and the like, comprise what is known as the "microbiome" of our aquariums.

A "microbiome", by definition, is defined as "...a community of microorganisms (such as bacteria, fungi, and viruses) that inhabit a particular environment." (according to Merriam-Webster)

Now, sure, every aquarium has a microbiome to a certain extent. The long-term successful botanical-style aquarium is 100% dependent upon the formation and growth of a healthy microbiome.

We have the beneficial bacteria which facilitate the nitrogen cycle, and play an indespensible role in the function of our little worlds. The botanical-style aquarium is no different; in fact, this is where I start wondering...It's the place where my basic high school and college elective-course biology falls away, and you get into more complex aspects of aquatic ecology in aquariums.

Yet, it's important to at least understand this concept as it can relate to aquariums. It's worth doing a bit of research and pondering. It'll educate you, challenge you, and make you a better overall aquarist. In this little blog, we can't possibly cover every aspect of this- but we can touch on a few broad points that are really fascinating and impactful.

So much of this process-and our understanding starts with...botanicals. 

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. Maybe a similar amount of seed pods. You might not even notice any difference..or you might see a .2 reduction in have to test. I recommend a digital pH meter for best accuracy. In fact, I recommend digital meters for almost everything, especially considering the tinted water which our aquariums feature, rendering the results of liquid test kits challenging to interpret.

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?

Personally, I've experienced far better results at manipulating pH in my water holding containers than I have in the aquarium. Of course, the dynamic of "transitioning" an aquarium from hard and alkaline to soft and acidic is a process which occurs in both the tank and the source water containers...

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-item 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!").

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 whatvarious 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!


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-testing 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 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 that 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! 

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. There are still many "unknowns" and no one 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.

This piece was, out of necessity, the most cursory look at this topic of "transitioning", but I hope it opens up more discussion on this seemingly popular topic within the aquarium community.

Stay excited. Stay conservative. Stay experimental. Stay diligent. Stay skeptical. Stay hopeful. Stay thoughtful...

And Stay Wet.

Scott Fellman

Tannin Aquatics 





Scott Fellman
Scott Fellman


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