Down and dark? A question from "the old mailbag..."

As you know by now, the world of botanical-style/blackwater aquariums has really started to explode over the past few years- emerging from a long period of time as a sort of "sideshow" in the aquarium hobby, and gradually becoming a viable and compelling approach to keeping a wide variety of fishes. 


And, as such, there has been a tremendous amount of confusion, speculation, and even downright misinformation out there on this topic. The good news is that we are seeing more and more aquarists venturing into this exciting area every day. Some of you have already been there, and more-or-less "have this stuff down cold", as they say.


That being said, we still receive a lot of questions from customers that can initiate good discussions which will benefit everyone. There is still so much room for everyone to contribute to our "art!" 


Here's a set of questions we received recently, which we think may answer some basic questions that many of you might have on a few subjects. We hope that you find this exchange useful!



We have some fish that prefer soft water. My ph is about 7.0-7.4, as we live in Texas with hard water. I have Catappa leaves and cones and a little peat granules in my canister. So it sister closer to ph of 7. We have killifish and Apistogramma. Since they are tank raised and tank bred fish, Changing my tank to a full on tannin tank, would it harm the fish more that be good for them?

Since they weren’t born into their natural soft waters, could me making their tank soft do them harm? I have a Fluval canister for my planted tank. It did come with all the bio media including charcoal. Is it best to remove the charcoal (Ed. note: this is a reference to activated carbon) so the tannin last longer or does it matter?


Also I have an RO drinking water system. Can I just use that water to do small partial water changes? That way the acclimation process would be slow (my RO doesn’t hold a lot of water) if so, will I need to use other additives to my tank if using RO water? Lastly, if I don’t have the RO/DI system is it still possible to keep my tank going as a soft water/tannin tank?


The idea of "repatriating" fishes to the conditions under which they have evolved for millennia is not really a problem. In fact, I have this theory that it's actually better for the fishes in the long run. My idea, as outlined before, is that you're not going to "erase"  a fish's genetic adaptation to a specific environment over millions of years of evolution in just a few generations of captive breeding. I can't help but wonder what the potential benefits might be from this practice.


However, you need to acclimate the fishes slowly and carefully, like you would any time you're acclimating fishes to conditions different than what they've been kept under previously. It's important to remember that fishes- even hardy, captive-bred ones, are stressed by rapid environmental changes, even to a more "natural" set of parameters. Take the time to do it right.


Keep in mind that the only way to actually soften the water would be to employ water which has been treated with reverse osmosis/deionization (RO/DI), as botanical materials cannot soften water. They might be able to reduce the pH somewhat in water with little to no carbonate hardness, but they cannot create massive overall parameter shifts.


Now, "color" is something that you can achieve by utilizing botanical materials in just about any type of water conditions. Remember, color is NOT indicative of the pH or hardness of your water. If you want to maximize the amount of color produced by the tannins in the botanicals, it's best to limit or eliminate the use of aggressive chemical media, like carbon, and use something a little less "adept" at removing them from the water, such as Seachem Renew, or some sort of ion exchange resins, etc.


Now, I personally DO use carbon in my blackwater aquariums in significantly smaller quantities than the manufacturers recommend, and have for decades in blackwater tanks, so I know that you CAN use it. You'll just sort of have to gauge for yourself how much is enough, lol.
No exact science here.


I would begin incorporating the RO water into your "makeup water" for your aquarium over time, as you described- a good strategy, IMHO. No need to rush. I personally have used straight RO/DI water in my tanks for decades...Some people use commercial products which add back some minerals, but I see that as a sort of unnecessary step (I mean, you're going to the trouble of removing all of the mineral content...LOL). Well, it makes sense for some fishes, like African cichlids, reef systems, etc., but if your goal is a blackwater aquarium with a lower pH and soft water, I'd personally avoid adding anything. Your substrate and/or rocks (if present in the tank) will add back plenty of minerals, IMHO.



If you don't utilize RO/DI, you can, of course, have a tank with "tinted" water; however, unless you have a means to create softer, acidic water, or if your tap water happens to be soft already, you'd likely have a pH of neutral to slightly alkaline at best. In my experience, you can't achieve lasting, stable, truly acidic pH levels with hard water. Again, there are "tinted" habitats in Nature which have harder, alkaline water, such as rivers and even brackish water systems. Leaves and other botanicals will impart color to the water regardless of its pH (again, color of the water is not a reliable indicator of pH or hardness...An "urban myth" in the blackwater aquarium world).


The most important takeaways from these very good questions are that it's important to understand some basics of water chemistry (something that always makes my head spin a bit...) and how various materials can impact the chemistry of the water. Take a few minutes to study this stuff, and you'll be better for it. There are numerous resources online and elsewhere offering great information about this stuff. Also, do make use of the substantial practical information we have right here in "The Tint!"


We hope that this little exchange has answered a few questions for you- or, even better- spurred you to do some additional investigation to add to your personal body of knowledge that can help you and others with this cool hobby niche!


Stay curious. Stay resourceful. Stay diligent. Stay creative...

And Stay Wet.


Scott Fellman

Tannin Aquatics 




Scott Fellman
Scott Fellman


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