Total confession: I am definitely not an aquatic plant guy. In fact, I'm not even able to identify half the plants out there that are popular at any given time, let alone the "classics" all that well...And the fancy "varietals?"
Yeah, forget about it!
That being said, I've kept plants all throughout my decades of life as an aquarium hobbyist. However, for me, the aquatic plant obsession bug just new bit. I don't know why. I love them. I think planted tank are amazing, and I respect and admire those who are good with them.
Yet, I look at planted tanks and I just don't feel this compulsion inside that screams, "I have to have one!"
Rather, I planted my flag in the "hardscape" department-specifically with botanicals and blackwater and such, and never really looked back. Now, I do currently have a blackwater aquarium with plants at home...And this is strange- it's probably my least interesting or compelling aquarium I maintain right now. Which is odd, because it's a great tank with lots of cool Southeast Asian fishes and tons of potential.
Yet, when I stare into this tank, I'm more likely to say "Meh!" than, "Wow!"
Now, my planted tank friends tell me that it's largely because I decided to go with notoriously slow-growing plants like Cryptocoryne...Plants that, without the addition of CO2 just sort of "exist", growing incredibly slowly. I mean, they look healthy and colorful, but they are just sort of...there. Of course, going with a large percentage of tissue-cultured plants (the freshwater equivalent of coral frags, IMHO) that were tiny to begin with didn't help, right?
So, this is as good a time as any to discuss the whole idea of plants in blackwater aquariums once again. (Yeah, we've had this discussion a few times!)
The interesting common denominator about this topic- like so many others when it comes to blackwater aquairums, is that there has simply been a lack of good information on the topic- and an abundance of speculation, assumption, and downright misinformation floating about out there in cyberland...
I think the misconception that plants can't grow in blackwater partially originates from the common "inflection point" of, "Blackwater aquariums are unstable/hard to manage/dark and foreboding", and merges with the well-trodden and partially factual "narrative" that says that, since many parts of say, the Rio Negro essentially have no plants, that plants can't live in any blackwater habitats.
I was able to glean some information that might be of use to you in this regard, and with all of the interest, it seems like an appropriate time to be discussing this stuff!
First, let's just clarify the "plants in Amazonia" thingy real fast.
There are two primary areas of interest in our particular "botanical-centric" habitat focus, besides just the better-known blackwater rivers, such as the Rio Negro, where plants are found.
The Varzea are seasonally-flooded forest areas, which are inundated by pH-neutral "whitewater" (ie; not significantly stained by tannins), and can reach significant depths, whereas the Igapo are generally shallow, blackwater environments with relatively low nutrient content and acidic soils. Varzea forests are extremely rich, which leads to a very rich aquatic ecosystem when inundated, and tend to have greater density of aquatic plants. Várzea forest soils have high nutrient contents because they receive high loads of sediment (from the Andean and pre-Andean regions) from the whitewater rivers nearby.
Igapó forests, by contrast, do not receive this seasonal influx of sediments , which is why they have relatively inorganic nutrient- poor soils. Igapo waters are acidic, with a pH ranging between 4 and 5, and are rich in organic materials- particularly humic and fulvic acids. It is also thought by scientists that the seasonal inundation of the Igapo soils creates anoxic conditions, limiting plant growth in general.
So, you CAN keep aquatic plants in blackwater aquaria intended to replicate, to some extent, either of these botanically-influenced habitats. Obviously, the Varzea-type flooded forests are more conducive to aquatic plant growth.
And here is the part which probably feeds into the general "you can't grow plants in blackwater" myth:
The other important factor affecting plant growth in these aquatic habitats is light; or specifically, light penetration. This affects diversity of both the terrestrial grasses and aquatic plants present in the waters. In the blackwater Igapo areas, light only penetrates down to depths of 1-2 meters, and many submerged grasses and terrestrial forest plants simply die back from lack of light. And the forest canopy adds to the shading in some areas, further reducing the amounts of light available to plants. Varzea tend to be more "open", and a greater abundance of light, and therefore, light penetration, occurs.
Of course, you can grow Amazonian plants in blackwater aquariums, such as the broad-leaved dwarf Amazon sword plant (Echinodorus quadricostatus), which prefers the dim conditions of blackwater rivers. And notice, I didn't even touch on Asian blackwater plants, like Bucephalandra, Cryptocoryne, etc.
If ever there were "poster children" for blackwater-native/tolerant aquatic plants, either of these two genera would be the ones.
Interesting to me is the use by many hobbyists of low pH substrates and leaf litter in their culture ( a lot of the blackwater Crypt. "players" use Catappa, etc. in a ground up form, almost like a "mulch" of sorts...A cool use for our "Mixed Leaf Media" and "MLM2", I'd say! ). Interestingly enough, many of the so-called "blackwater Crypts" also tend to "melt" if they are in soils that are too nutrient rich...A lot to take in here, but a lot which plays right into our fascination with botanical-style blackwater aquariums!
And what about Africa? It's more than just Anubias...
I think that a considerable amount of time needs to be spent by members of our community simply reaching out to our friends who are into aquatic plants...the knowledge and commonalities are remarkable. We simply need to discuss and understand the realities of keeping plants in blackwater versus the more "traditional" " clearwater" aquarium.
It's a known fact that light doesn't penetrate as effectively in the tinted water of blackwater environments. That's ONE of the reasons you don't see a lot of algae in many blackwater systems. And floating plants, of course, tend to do well-because you don't really have the "light penetration factor" influencing them as much as say, rooted plants. Light penetration is a limiting factor, other things being "more-or-less" equal, right?
Well, yeah...you can compensate with brighter light...the beauty of LEDs, right? And of course, just having light in our tanks isn't enough.
The other big issue to tackle when keeping aquatic plants in blackwater aquariums is to some extent, the well-trodden opinion that blackwater may be described as more "nutrient poor", and having much lower ionic concentrations of calcium, magnesium, sodium, and potassium than clearwater environments.
So how do you overcome this?
You fertilize your tank- just like you do in a "clearwater" system. You'll probably have to adjust your doses to compensate for the near lack of the above-referenced major ions, but it's pretty much that simple, in my experience. You'll use more fertilizers. And if you're growing plants that rely on rich substrates, like Cryptocoryne, I've found that you really don't have to do all that much differently than you do in a "clearwater" tank.
So, just because the water is dark, doesn't mean you can't keep plants. And hey, if you're a guy like me, who's obsession is with brown instead of green, it simply means that there are lots of different directions you can go in our world.
Stay curious. Stay motivated. Stay diligent. Stay undaunted...
And Stay Wet.