A couple of questions...a bunch of areas to explore!

As you are probably acutely aware by now, we receive a lot of questions, via email, PM, etc. about our vision of blackwater/botanical-style aquariums! It's actually one of the best parts of running a business like this- really getting "down and dirty" into the real questions that fellow hobbyists have about this stuff! 

Periodically, we receive some email which have questions from which a large number of our community members could benefit from seeing answered. Today, we'll feature one such email query (name omitted for privacy, of course), edited a bit for ease of reading!

It was really a great cross-section of questions and concerns that we've all had from time to time, so here we go!

From my reading I see that leaf litter decomposes and breaks down in a matter of weeks, and needs to be replaced. No problem, but what does the decomposition do to your tank & water parameters?   Does it just get filtered out by the things you mentioned (Seachem Renew, etc) ?


That is correct! Leaves and other botanicals will break down over weeks or months (depending upon a variety of factors, such as water chemistry, the degree to which they were prepared prior to being placed in the aquarium, and if you have fishes which graze on or nibble directly on them! 

From a chemical standpoint, as aquarists, we are wise to consider what exactly all of the decomposition does to water quality. Here's where it gets kind of interesting, IMHO. Now, initially, especially in a new tank with immature/incomplete nutrient export capabilities, or in a long-established, stable aquarium, adding a large influx of botanicals can cause some short-term changes to the environment. Immediate possibilities in extreme cases could be a reduction or depletion of dissolved oxygen caused by bacteria growth. This is a rather "extreme" example, though- and usually happens when you dump a lot of material in all at once.

Typically, you'll add materials gradually, to allow the bacterial and fungal populations of the aquarium to grow and adjust to the influx. And curiously- over time, it seems that most of us see no significant increase in nitrate, phosphate, etc. as a result of this material being present in the water. It seems that the botanical materials might serve a dual purpose of fueling bacterial growth and providing -maybe?- some form of biological filtration...you know, creating a substrate for them to grow on...kind of like live rock in a reef aquarium...a sort of "on board" bio filtration media and carbon source- all in one? Just a theory I have had bouncing around in my head, but the results we are seeing in our tanks worldwide are making me think about it more seriously all the time! 

I have read that when you deal with very soft water the ph can swing or drop because of no buffer in water. Do the tannins or wood help this or is it smart to have a couple rocks or something that adds a little KH to keep the ph and softness stable??  Or am I overthinking this. I need to take current readings of my tap water and see what starting point is.  

The idea of pH impact/swings as a result of botanical materials present in the water with minimal carbonate hardness is a distinct possibility. However, one of the things I've personally found is that the impact on pH created by botanicals, in may cases, is surprisingly limited. Sure, the pH can and often does drop significantly, depending upon both the starting pH/hardness of the tank water, and the amount and type of materials incorporated into the display. For example, many leaves or materials like catappa bark will have far greater impact on the pH than more "durable" materials, like "Jungle Pods", etc.

The wood will impart tannins into the water (which will visually "tint" the water, as we've seen many times), the amount of which is largely dependent upon the wood itself. We have no real definitive stuff to draw upon, but anecdotally (damn, we have to use that a lot, huh?), one could see visually the amount of "tint" imparted varies from wood type to wood type a little bit. 

As far as "swings" in pH- I've not personally experienced this phenomenon, which is not to say that it isn't something that happens. I have seen trends up or down over time, and of course, the usual day/night pH fluctuations which have nothing to do with botanicals, but I haven't seen wild environmental fluctuations in botanical style, blackwater aquariums. Usually, once you have completed the additions of botanical materials to your aquarium, you'll see a slight trend downward in conditions which  are amicable to this (i.e.; low to negligible carbonate hardness).

However, one of the things we've noted is that many aquarists are actually surprised by how little the pH is impacted by botanicals! Even with pure RO/DI water, like I use, and lots of wood and botanicals, I've found that the pH in my tanks tends to find a range (within like .1 or .2, BTW) and stays there. In my instance, it's about 6.5-6.6. In fact, It's tough for me to get it much lower. I think, as you've alluded to, that the use of substrate materials, such as sand and rocks, may provide significant enough "buffering capacity" to keep the ph confined to a narrow range. Now, many of us have started experimenting with purely botanical substrates, creating a different and potentially more "aggressive" pH influence capacity...something we can come back to in the future!

Your last sentence hit the nail on the head: We need to test our source water, and our aquarium water on a regular, continuous basis, particularly for pH, hardness, nitrate, and phosphate. It's a foundational skill, and really, a responsibility of all who want to play in this arena. Studying these parameters regularly will give us a good snapshot of where our tanks are now, and where they were...and possibly, when enough data is accumulated- an idea of where they're headed! Trends are important, and there is simply no substitute for understanding the water chemistry in our aquariums.

And the other important thing is that there is no "recipe" by which we can dial in exactly the pH/hardness and/or other parameters we want. It requires observation, testing, and on occasion, intervention to get what we want.

Yes, principles of chemistry apply to everything, but every tank has a myriad of random factors which can impact the pH and other parameters. We can speak in generalizations when discussing how to manipulate or impact water parameters, but we really can't do the same about how much we need to do to achieve specific results. The old adage of "test, then tweak" is really the way forward here!

There is so much to learn, so much to practice, and much to share. Many of the principles of aquarium environmental manipulation and long-term management have not changed over the century or so of the modern aquarium hobby's existence. What has changed is our ability to study them and utilize different techniques and materials to accomplish things. 

In the end, it's about learning, experimenting, interpreting, and sharing.

We've all got a lot of work to do, huh?

Stay excited. Stay observant. Stay informed. Stay curious...

And Stay Wet.

Scott Fellman

Tannin Aquatics 

Scott Fellman
Scott Fellman


Leave a comment