With our emphasis on replicating many aspects of Nature, on both an aesthetic and a functional basis- we touch on a lot of ideas and techniques on how to accomplish this process in our aquariums. However, one of the least-discussed topics is...lighting.
Now, I'm probably not the best person to discuss many aspects of aquarium lighting with, yet being a long-time reef aquarist and former commercial coral propagator, having at least a basic understanding the ideas and practical applications of lighting in our closed aquatic systems is a core requirement for success.
Of course, in our aquariums, which typically emphasize botanicals, wood, and even rocks over growing live plants, lighting tends to be more of an aesthetic consideration than a primary necessity for creating optimal conditions in our aquariums.
Indeed, the tinted, blackwater habitats that we seem to gravitate towards in our world generally don't have huge stands of truly aquatic plants. This is due to factors other than just light conditions, such as the topography, the ionic composition of the water, and the geology of some of the regions that we tend to replicate in our aquariums. That being said, light penetration and overall lighting conditions in the natural aquatic habitats that we are fascinated by are interesting and important aspects to consider in our aquariums.
In a typical rain forest, it's estimated that as little as 5% of the sunlight reaches the "floor", so it goes without saying that any stream or creek under the canopy of trees is not getting that much light! If aquatic plants are present in these habitats, they're typically species that can adapt to lower lighting conditions.
And, in the aquarium, they tend to do well in lower-light conditions. There are other systems which, despite their tinted blackwater conditions, are exposed to tremendous sunlight intensity, and foster significant aquarist plant growth, such as those found in rivers in tropical Africa.
As always, research about the habitat you're interested in replicating in your aquarium is so important.
Now, of course, lighting is just one part of the picture (with nutrition and fertilization being some of the other important parts), but it plays a huge role in our success with plants in blackwater aquariums.
For a very long time, hardcore planted aquarium enthusiasts have been a bit intimidated by the idea of blackwater planted tanks, because of the concerns over sufficient light penetration into the tinted water. With a greater understanding of the overall blackwater environments and their propensity to grow certain plants, it's more of a matter of figuring out how to maximize lighting intensity to assure that sufficient quantities of light reach our plants.
This affects diversity of both the terrestrial grasses and aquatic plants present in the natural waters. In the blackwater Amazonian Igapo areas that we obsess over, 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 aquatic plants in blackwater aquariums, such as the broad-leaved dwarf Amazon sword plant (Echinodorus quadricostatus), which prefers the dim conditions of blackwater rivers.
As mentioned above there is one area which comes to mind immediately when we talk of blackwater habitats with aquatic plants: Southeast Asia- particularly, Borneo.
And when we think of Borneo, what comes to mind more than the darling of the plant world, Bucephalandra? And of course, my personal fave family of plants, Cryptocoryne. If ever there were "poster children" for blackwater-native/tolerant aquatic plants, either of these two genera would be the ones.
"Generically speaking", 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...that's the beauty of LEDs, right? And of course, as alluded to above, 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.
One thing you won't hear me talking about is the use of CO2. Not because I don't recommend it or believe in it- it's simply because I don't personally have a lot of experience with using it...That being said, I have many friends who use CO2 in blackwater tanks with a tremendous degree of success...
I think the job I'll continue to take on here at Tannin will be to encourage aquatic plant enthusiasts, and those who want to keep aquatic plants in blackwater aquariums- to go for it and do great work.
The simple reality is that you absolutely can keep a lot of aquatic plants in blackwater tanks, with tremendous success. It's simply a matter of compensating for the environmental parameters which need to be augmented (ie; lighting, fertilization...), and doing what you already know how to do. If you're into environmental/biotopic authenticity, you'd want to look at what plants are found where, of course- but the bottom line is that the variety of plants that you can keep in generic blackwater aquariums is significant!
Now, if aquatic plants are not the primary focus of our blackwater/botanical-style aquariums, lighting becomes more of an aesthetic consideration than just about anything else.
So, it goes without saying that in an aquarium where you're trying to replicate one of those hidden "igarapes" (literally "Canoe Way" in the indigenous language of the region), without a diversity of light-demanding aquatic plants, you really don't need to worry about providing a ton of bright light.
Rather, it would make more sense to apply "spot" lighting or dimmed lighting from a format like LED, which gives you more control over color and intensity than most other lighting methods. Or, you can use "room ambient" lighting and call it a day!
There is so much to learn from managing a system set up to replicate one of these environments, and it is helpful to look to nature once again to help us make decisions. Without tons of excess light hitting your aquarium, the incidence of excessive algal growth is definitely limited, which is important when you take into account the decaying leaves and other botanical materials present in these environments.
So, where does this leave us?
Well, for one thing, it leaves us the opportunity to explore and interpret the deep, dark habitats which we find so alluring.
That's a pretty serious challenge, right?
Stay inquisitive. Stay excited. Stay open-minded. Stay creative...
And Stay Wet.