As aquarium hobbyists, we tend to get caught up in the minutiae of "stuff" involved in setting up an aquarium, and tend to concentrate on those areas that are most important to us. And it's nice to see more hobbyists getting really into the details on the use of botanicals in their aquariums. We're starting to see more and more use of certain materials for specific fishes, and as more and more fish geeks start seeing some interesting effects, the "buzz" on them grows a bit louder.
We receive a lot of questions about which botanicals would be best suited for a given fish. These are really great questions, because they show me that we're at a phase where hobbyists are not sending to be "sold" on the concept of using botanicals in their aquariums- they're now down to "brass tacks", trying to figure out exactly which botanical is best for their situation.
Here's the real quick and dirty, shotgun-style answer, by the way:
Pretty much any of our botanicals will "work" with any fish that you keep.
I mean, sure, you probably aren't going to want to keep your Haplochromis from Lake Malawi in a tank loaded with catappa and guava leaves. However, for the most part, to the fishes, a botanical is a botanical is a botanical. A characin from the Amazon isn't likely to be any less healthy and happy because his aquarium has a healthy load of Banana Stem pieces, Jackfruit leaves, or a selection of "Savu Pods", as long as the other requirements for his/her care are met. The botanical items provide a place to hide, foraging, and a "substrate" for algae an biofilms to flourish on. The fish are likely indifferent to the physical attributes of the specific botanicals, with the exception of those who use some of the pods for shelter, or for a spawning cave, such as Apistos and other dwarf cichlids. Then again, these fishes spawn in clay pots, too, so...
This is hardly a scientific statement (nor earth-shattering), but... it's my opinion that most any botanical item will impart some tannins and other humic substances into the water, the degree to which is dependent upon many factors.
Based on my personal experience, I've always felt that materials like seed pods, stems, etc., are secondary to items like leaves and bark in terms of their pH-reduction abilities and overall environmental impact. This is largely anecdotal, based on personal observations in aquariums, not some controlled lab setting. In general, my experiences and those of others seem to confirm that various leaves and cones (like Alder) seem to have more profound water-tinting and pH-reducing effects (in a soft water setting) than the (harder) botanicals like seed pods, etc. Perhaps this is because they can more easily release tannins bound up in their tissues, which have more noticable impact on pH in a soft-water setting.(the soft water thing is a definite "qualifier", IMHO).
This is not a revolutionary disclosure, as various leaves have been offered for years to aquarium hobbyists for the primary purpose of pH reduction and tannin "impartation." Of course, much has been written by various parties of the "near miraculous" attributes of some of them, such as Catappa leaves, which has always given me pause. (Okay, it's made me squirm a bit, too.)
As we've discussed many times, leaves and other botanical materials will have different effects in different situations. If your water is hard and alkaline, steeping a bunch of catappa leaves will definitely color the water. It will likely have a small impact on the pH (depending upon the starting pH and the KH of the water. The impact on KH will be minimal. You won't get "Instant Igarape" by dumping a half a pound of leaves into your aquarium filled with hard, alkaline tap water! (oh, product idea! LOL)
My personal practice has been to use straight RO water for my blackwater aquariums, which many hobbyists are adverse to doing, btw, because of fears over it's lack of buffering. As a result, my water conditions are apparently pretty easy to impact, in my experience. We all have to have our comfort zones, so I couldn't criticize you in the least if you use buffered RO. My personal experience has been that, even in the most botanical-laden tank I've ever maintained, when starting with pure RO, the TDS reading has always hovered around 12-14, and I have enjoyed good overall stability. I simply have not had crazy fluctuating parameters or any of the other scary things many attribute to the use of straight RO.
It's probably the old reefer in me, but I personally find it very comforting to know exactly where I'm starting, chemistry-wise, so RO to me is perfect, lol. Regardless, this is a topic that is wide-open for debate and experimentation, and my practice is definitely not "recommended"...it simply works for me.
One interesting observation I've made: I always found the TDS reading in my tanks to be surprising; I expected much higher, thinking to myself, "You'd think that all of the stuff being released from decomposing leaves and botanicals would have a significant TDS impact, right?"
Not being an environmental chemist, I'm really not qualified to make any kinds of blanket statements on the specific chemical impacts of various botanicals. I can only go on personal experience and that of my friends and our global community of blackwater aquarium enthusiasts. I use and have used everything that we offer in my own aquarium for years with good results. And my experience has shown that botanical items in a responsibly-managed aquarium can have many positive impacts on their inhabitants (coloration, behavior, overall health, and in some instances, hobbyists have implied that spawning occurs more readily).
Scientific research has definitely confirmed that humic substances play a huge role in fish health, so that part is not entirely surprising. I'm pretty confident in ascribing many of the other "benefits" to good overall aquarium management, including the use of botanical materials to shift environmental conditions towards those found in the native habitats of many fishes. The "spawning" thing is one that I personally feel is more of a result of excellent care, with the botanicals perhaps "pushing them over the edge." It would be naive for me to assert that the botanicals were the "It Factor" in the success of any aquarium or breeding experiment.
In the end, I think it's safe to say that the use of botanical items as a chemical, "structural", functional AND aesthetic enhancement to the aquarium environment is as legitimate and valid as anything else we do. They're having a noticeable impact on the hobby right now, and there is a lot of "buzz" about them. However, I think that it's important for all of us to study what we can find about the natural habitats of our fishes, from both an academic and practical standpoint. This is a great starting point for anyone who wants to attempt to replicate a more natural ecological niche in their home aquairum.
We can read all of the "marketing talk" (by myself and others), but we should really take that with a "grain of salt", and draw our own conclusions from the personal use of these materials in our own aquariums.
That being said, I DO know this cool website where you can purchase some of this stuff to experiment for yourself... :)
Stay curious. Stay bold. Stay challenged. Stay smart.
And Stay Wet.