The light stuff...

We obsess over some crazy stuff in our world of botanical-style, blackwater/brackish aquariums, don't we?  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

We receive a LOT of questions about lighting...specifically about how you can grow plants in blackwater, botanical-style aquariums, and what type, intensity, and duration to use.

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, I've long believed that having at least a basic understanding of the ideas and practical applications of lighting in our closed aquatic systems is a core requirement for success.

Lighting is a big deal I the coral world.

In the reef aquarium world in general, lighting is essential, as it powers photosynthesis within the zooxanthellae (symbiotic algae) which are found in coral tissues. It's pretty much fundamental stuff, and we are indoctrinated from day one in the hobby to embrace lighting and its importance to our systems.

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, rather than a primary necessity for creating optimal conditions in our aquariums.

And it also compels us to turn once again to Nature for some cues...

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. They create not only an interesting look, they can provide supportive intensity and spectrum for certain types of plants, like Mangroves.

In a typical tropical rain forest, it's estimated that as little as 5% of the sunlight reaches the forest "floor", so it goes without saying that any stream or creek under the canopy of trees is not getting a ton of light! If aquatic plants are present in these habitats, they're typically species that can adapt to lower lighting conditions. 

Of course, "lower light levels" in Nature is still a lot more light than you might think- and a lot more than we typically will think of in the aquarium context. We tend to measure light intensity in photosynthetically active radiation (PAR), which gives us a "value" to measure and relate to.

The "architecture" of tropical forests are determined by the vegetation's need for sunlight. There is tremendous competition among rain forest plants for this vital energy. Trees grow very tall, and  don’t waste energy on producing branches until they reach the canopy, and are able to compete successfully with other trees for the available light.

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, researching 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 were 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.

Light penetration IS a big deal...perhaps the most important of all factors which determines the ability of aquatic plants to grow in blackwater habitats (along with nutrient-rich substrates). Light penetration 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. Well, that and the fact that they're submerged terrestrial plants, right? They could only hang on for so long anyways! 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", 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...there are things you can do to make up the difference... 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 blackwater aquariums isn't enough. Now, you certainly CAN rely on room ambient light for some situations, and supplement lighting where needed... It's important to consider the types of plants you're dealing with, and what your goal is for the system you're creating.

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.

Of course, many of us play with "hardscape only" types of tanks, and lighting is really more of an aesthetic choice. 

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. In fact, although I've played with just about every type of lighting format out there, I've repeatedly turned to LED as my "go to" for about a decade now. Coming from the reef world, we were always a bit amused that LED lighting took years to catch on in the FW world at any scale. It's so versatile and configurable, that it makes perfect sense in virtually every application, from "nutritive" and plant-growth focused to purely aesthetic.

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.

Of course, if you ramp up the lighting intensity (easy to do with LED's), you can certainly grow a lot of nuisance algae! We all know that light+nutrients= algae, right?  Yup. I've deliberately "over-illuminated" botanically-rich aquariums for the sole purpose of seeing how much I could apply without creating an algae nightmare....Like, full intensity on high-output, full spectrum, 40 watt LED over a "nano tank"...that kind of "over illumination!"

It grows algae. Even in "tinted" water.

So, when I hear hobbyists proffering that you can't grow plants in blackwater, I call foul. You certainly can. It's all about the technique...and the other factors which are at play.

And yet, I've experienced no more occurrence of algae in the leaf litter tanks than I have in other setups, when lighting is intelligently and thoughtfully applied. On the other hand, regardless of what type of system I work with, I'm fanatical about husbandry and nutrient control/export...obviously, another key factor.

While it would be intellectually dishonest (and just plain untrue) for me to assert that blackwater/botanical-style aquariums aren't susceptible to algae outbreaks, it is sort of remarkable that we simply don't have massive algae issues in these types of aquariums on a regular basis.

I think the main reason why we don't see massive algae issues is because we as a community have placed so much emphasis on the techniques of aquarium husbandry/management- specifically, the need to embrace nutrient control and export techniques. 

So, as usual, I rambled all over the place, with bits and pieces of different ideas woven loosely together...I suppose the biggest takeaways here are:

1) You can grow plants in aquariums with tinted water (with proper lighting, in terms of spectrum, intensity, and duration) 

2) You can grow algae in aquariums which you seriously over-illuminate, or ones which you more modestly light and don't apply proper husbandry techniques to.

3) Our recommended lighting form factor is LED, because of its versatility and adjustability.


There is so much more to explore here, in terms of lighting and botanical-style aquairums. Lessons to learn, experiments to undertake, breakthroughs to achieve, and even mistakes to be made. 

Stay inquisitive. Stay excited. Stay open-minded. Stay creative. Stay observant...

And Stay Wet.


Scott Fellman

Tannin Aquatics 

Scott Fellman
Scott Fellman


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