Blowing up Brackish

One of the great things about the aquairum hobby is that there are so many directions you can take to enjoy it. So many different avenues to explore. One of the hobby's most neglected speciality areas is brackish water aquariums.

Yes, brackish. And yeah..neglected...As in not done by a lot of people.

Okay, let me clarify: Lots of hobbyists have played with brackish water tanks over the years; however, the reality is that brackish has been pretty much neglected by the mainstream of the hobby. How neglected? Well,  brackish aquariums make blackwater aquariums seem downright popular by comparison!

Yeah, brackish. As in, brackish water aquariums; mangrove estuaries, intertidal habitats...

Over the years, I've become quite familiar with these habitats, both as an aquarist and as a traveler, having spent many happy hours in stinky, mosquito-filled tropical backwaters, often knee-deep in mucky soil, poking around the mangroves with the delight that only a fish geek can bring!

I had kept brackish tanks for years...a natural compliment to the reef tanks I'd been obsessed with. And it always seemed like a good way to transition from the coral world, at least!  I figured that the "Tannin thing" would come later, a natural "digression" from salt-sequentially, if you will. Brackish always made sense for someone who had his head firmly in the saltwater world for decades, both as a hobbyist and later, as a business person.

Yet, it's at this point that I should address the common misconception that brackish water aquariums are like "reef aquariums lite" or somehow this easy-breezy training ground for saltwater aquariums. It's not. It's a separate "thing." Now, brackish water aquariums do involve some skills that might be of use in marine aquarium adventures, such as preparing and measuring saltwater, managing evaporation. and maintaining water quality in a dynamic, ever-changing system. 

Yet, have no illusions. It ends with that, IMHO. Brackish water aquariums are really  not a "gateway to saltwater." In fact, I'd wager that a high percentage of the few aquarists who have played with brackish water aquariums have never kept a reef tank. So, I think that we could get that idea out of our heads once and for all.


Not much more difficult than any other type of aquarium, really. You just need to learn the "operating system." 

Then why aren't brackish water tanks more popular?

Brackish water (arguably possessing a specific gravity of 1.005-1.010) is a sort of "middle ground" that for decades in the hobby has not been well-travelled. And widely mis-understood. I've played with brackish water for almost two decades, in between reef keeping and my blackwater/botanical-style aquarium stuff, and in researching both the hobby work that has been done, and the scientific materials out there on the wild habitats, I have sort of made this conclusion that it's simply been an afterthought, at best for aquarists.

Although there is a good amount of scientific information about the brackish-water habitats from which brackish water fishes come, in the hobby, (with the rare exception of some biotope enthusiasts) we've sort of distilled brackish-water aquarium "aesthetics" down to white aragonite sand, a few rocks, and maybe some hardy plants...and it's been mired in that aesthetic hell for decades.

And again, it all goes back to that "perception" thing...

I think that the perception among many aquarium hobbyists has been that brackish is more" tricky" to keep than freshwater, easier than a reef tank, yet offers little in the way of excitement on first glance to make it worth the effort. I mean, the fish selection and availability to the hobby has not exactly been stellar, with many dealers hesitant to stock many brackish fishes for simple lack of demand and interest. Some, like Scats and Monos, simply get too large to be candidates for many hobbyists' aquariums. Others are just not widely understood to be brackish dwellers.

And quite frankly, many fishes that have been perceived to be "brackish" by hobbyists are either actually from pure freshwater habitats (I'm thinking about certain Glassfish and some Rainbows), or have some populations that are from brackish (which are seldom imported). And then there are those fishes, like Mollies or Endler's Livebearers, which are Euryhaline (capable of tolerating a wide range of salt concentrations), with the majority of the wild populations being found in pure freshwater. 

Salt, in many cases, is simply used for health purposes by breeders.


When I started working with brackish again a few years back after a long break, the idea, was to demonstrate how we could bring some new life and a slightly more realistic approach to the rather staid, traditional brackish water aquarium as the hobby knows it. Of course, our "slightly more realistic approach" is actually somewhat of a radical departure from the usual brackish water tanks which have dominated this obscure niche for decades.

As a decades-long reef aquarist and blackwater, botanical-style aquarist, how could I resist a "fusion" of the two? Besides, it was another example of the world being the way it really is, and how we as hobbyists chose to interpret it in our aquairums. And I personally felt/feel that we've been sort of choosing the safe, "established", generally unrealistic, and altogether boring path in brackish for decades! 

That doesn't cut it.

So, I had this idea to portray the brackish environment as it really is...not some sanitized, "aquarium aesthetic" version. And of course, as you know, if an idea is a bit out of the norm, we're all over it! It was time to "evolve" brackish aquariums into something that put function first.

And when an idea like an "evolved brackish system" pops into our heads, it's time to give it a whirl, as they say.

And it starts with a few important pieces of hardware; some stable environmental parameters, and patience...

There are several physical materials that are the basis for our concept of the "evolved" brackish-water aquarium:

-Mangrove branches

-Rich substrate

-Mangrove propagules

-Mangrove leaf litter

These are all things that we've touched in detail over the years in "The Tint", so I won't reply touch on them individually too much in the context of this piece...We'll revisit each again for sure in the future, however!

Let's talk about the operating parameters used in our approach, for just a second. And of course, it all starts with salt, right?

We initially targeted a specific gravity of 1.004. That is a sort of "average" of some of the habitats which I have studied over the years. However, for a variety of reasons, over the lifetime of my aquariums, I often migrated the specific gravity up to 1.010. People ask me a lot what set to use. I use Tropic Marin salt mix to achieve this. It's been my "go-to" salt brand for almost two decades. There are many other fine salt mixes out there...You can use any one of 'em. Just choose on and stick with it.

So, one consideration in keeping a brackish tank; indeed, replicating a brackish habitat- is that they it's a surprisingly dynamic one, subject to tidal influences (impacting specific gravity, temperature, and turbidity) and other environmental variations, like current and light penetration. And, in our approach, the influence of botanical materials, substrate, and mangroves is another factor to consider.

So, although maintaining an absolutely rock steady specific gravity is admirable, it's not absolutely mandatory for success. Stability within a range is more important in brackish, IMHO.

Oh, by the way, my fave piece of testing equipment for specific gravity is a digital eliminates any "interpretation" and guesswork when you're trying to determine the lower specific gravity levels that we play with! Swing arm hydrometers and the floating varieties work just fine, yet are prone to losing calibration and giving erroneous results easily.

So,  why not drop a few extra bucks and get something which is ridiculously accurate once and for all? If you're going to play in this "slightly salty" world, a digital refractometer is a great investment!

We maintain the specific gravity consistent by use of a very simple automated top-off system, the "Smart ATO Micro", which consists of an optical sensor, which you place in your tank at the depth you want the water level to remain at. When the system detects that the water level has dropped, it activates a tiny but incredibly powerful DC pump, which you place in a reservoir or other container below the tank, filled with fresh water.

There are other auto top-off systems which you can use. And of course, you can go manually, but the automated way is much easier, IMHO.

Other parameters?

I shoot for a water temperature is 77.5 F /25.2C. The typical pH of the water in my brackish tanks is 7.6-7.8, and the KH is 7.  These are not "absolutes" or "recommended parameters"- these are just the ones that my tanks are kept at. An interesting set of readings...And we can talk more about this stuff in a future installment of "The Tint", as it's probably worth more discussion! 

Water chemistry in brackish water habitats is influenced by many things, including the substrate, accumulation of botanical materials, the presence of mangroves, and the influence of ocean waters.

Interestingly, however, this type of system runs much like the freshwater botanical-style systems that we are used to, with the exception that it is likely more "nutrient rich" than the typical botanical-style tanks we play with here. The dynamics of decomposition and the ephemeral nature of leaves and such in the water are analogous in many respects, as well.

Our natural "muse" is the mangrove ecosystem.

And of course, there are a few components which, in our opinion, "power" the brackish water, botanical-style system: Mud, leaf litter...and mangroves.

The complex ecology of these natural ecosystems is as fundamental to our aquarium approach as it is in the freshwater botanical-style systems we're more familiar with.

Fungi and bacteria in brackish and saltwater mangrove ecosystems help facilitate the decomposition of mangrove material, just like in their pure freshwater counterparts. Interestingly, in scientific surveys, it's been determined that bacterial counts are generally higher on attached mangrove leaves than they are on freshly-fallen leaf litter.

This is kind of interesting, because ecologists feel that attached, undamaged mangroves leaves don't release much tannin, which, as we know might have some ate-bacterial properties. However, it's also been found that materials like humic acid, which are abundant in the mangroves, stimulate phytoplankton growth there. 

Interesting, right?

The leaves of mangroves, as they break down, become subject to both leaching of the compounds in their tissues, as well as microbial breakdown. Compounds like potassium and carbohydrates are commonly leached quickly, followed by tannins. Fungi are the "first responders" to leaf drop in mangrove communities, followed by bacteria, which serve to break down the leaves further.

So, in summary, you have a very active microbial community in a brackish water aquarium. 

And the idea of a rich, sedimented substrate has been another "backbone" of our approach to brackish water aquariums. Our systems revolve around the growth of mangroves, which need these types of substrates. But it's not just for the mangroves that we incorporate them in our tanks.

We've utilized a very rich mix of aquatic soils, similar to what has been used in "dirted" tanks by aquatic plant geeks, yet with a buffering component (finer, aragonite or calcareous substrates) and commercially-available marine biosediment materials.  We created a "workable" environment to grow mangroves with such a substrate.  

And by managing the water quality with regular, frequent water changes, and careful, automated topoff to keep specific gravity constant within a range at a brackish level (like-this is a fundamental thing), I believe that we have been able to simulate this environment on at least a superficially functional level.

Kind of like what we're doing with our freshwater leaf-litter-bed aquariums?

I wanted to create a functional mud-like substrate that would facilitate both denitrification and the ability to  provide a habitat for minute life forms. I spent a lot of time playing with different mixes of sediments, muds, sands, and soils to create what I feel is a great brackish-water mangrove habitat substrate. We have formulated it to be included in our NatureBase line under the product name, "Mangla."

I felt that this substrate would provide a more natural setting, and would facilitate more natural ecological function for a brackish water aquarium. My original intent was to plant some Cryptocoryne ciliata, a species well-known for its ability to adapt to a low salinity brackish-water environment.

I just couldn't do it, lol.

I couldn't help but to focus on my first love, mangroves, employing some fresh propagules, and to increase the specific gravity of the aquarium to 1.010, considerably higher than the documented SG at which C. ciliata is known to survive (typically 1.002-1.005).

The second reason for employing such a rich substrate in a "non-planted"  aquarium such as this was to set up the system in anticipation of the time when the mangrove propagules, which I anchored to the upper part of a dead mangrove root/branch "structure", would put down prop roots and ultimately "touch down" and penetrate the substrate layer. I knew this process would take many months, of course, given the depth of the tank.

Patience is another key ingredient in the brackish water aquairum which employs mangroves.

I also added some dried Malaysian Yellow Mangrove leaves to the surface of the substrate, with the intention of letting them do their thing and decompose on the substrate and "do their thing" to help enrich the habitat with tannins and humic substances. A crew of Olive Nerites snails was added to the system as a means to control algae and "work over" the decomposing leaves, and they are remarkable for their ability to do both. 

So, what we typically see over the first six or so months of most of our aquarium's existence is the development of a remarkably stable, biologically active, and rich habitat. The mangroves do just what I thought they'd do in these cirumstances: They put down prop roots, and grow many leaves, some of which do dry up and fall...and of course, we do allow the leaves to accumulate on the bottom, just like in the natural habitats we are attempting to replicate to a certain extent.

The nutrients the mangroves seek lie near the surface of the mud, deposited by the tides. Since there is essentially no oxygen available in the mud, there is no point in the mangroves sending down really deep roots. Instead, they send out what are called "aerial roots" (that's what gives them their cool appearance, BTW), sort of "hanging on" in the mud, which also gives the mangroves the appearance of "walking on water."

And of course, when the leaves and other mangrove materials break down, they form detritus.

In wild mangrove habitats  a significant amount of detritus is readily consumed by a group of specialized animals and fishes before it is being rematerialized completely in to inorganic nutrient form. And production and accumulation of detritus in these systems has been correlated by scientists to increased growth of the mangroves themselves.

Now, interestingly enough, as I've experienced with my freshwater, botanical-style aquariums, I've seen a remarkable stability in terms of the environmental parameters, and a definite solid growth in the mangrove seedlings I grow, which is especially impressive once the roots begin "touching down" and penetrating into the substrate layer.

What I'm seeing over and over in these systems- and what I planned on seeing before I took this approach- is that the substrate plays a very important role in the overall setup.With the mangroves growing at a significant pace, laying down thicker and thicker root structures.

I am very diligent about not overfeeding my brackish tanks, but I do little to no siphoning of the substrate. Even the nutrient-rich fecal pellets of the snails are allowed to accumulate...Yeah, this is a far, far different approach than I've ever taken with any aquarium! Almost contrary to anything I've done before with other types of aquarium systems.

And I'm okay with that.

Although it seems very weird simply stating, "I'm not siphoning the bottom of my aquarium and allowing the detritus produced by decomposing leaves and such to accumulate." - I have no particular feelings of negativity attributed to this practice. I'm quite okay with it, because it's a well-managed aquarium, with the other basics of aquarium husbandry attended to.

As I've talked about so many times here, detritus is not the nightmare that we make it out to be. Remember, the idea is that we're trying to work with the micro and microfauna which reside on the substrate, and to deprive them of their food  source is, well, problematic if that's the end game, right?

It's about cultivating life forms throughout the ecosystem.

This type of brackish water aquarium is truly one of the most stable, easy-to-maintain systems I've ever kept. And really, everything has been remarkably predictable! The biggest surprise was the very rapid establishment of the mangroves- in particular, the robust development of the leaves.

And really, the idea of creating and managing a little ecosystem is simply not that new to us; it's simply being applied to a different type of aquarium. 


I think that the current "version" of brackish water aquariums as presented in the aquarium hobby  is a good part of why they've remained relatively obscure for so long...they are, well...kind of monochromatic, shockingly unrealistic, and dare I say, boring! Sure, there are always exceptions, but the majority of brackish tanks I've seen set up in that manner have, IMHO, left little to generate more than an occasional acknowledgment from the aquarium world at large.

I think we can/will do better.


Like anything else in the hobby, brackish water aquariums require little research, work, understanding of the natural habitats that we're trying to replicate...and a lot of patience. Pushing in a new direction in this rather obscure niche will require everyone who plays in it to bring a sense of adventure, experimentation, and purpose. 

And the rewards will be rich. The secrets revealed game changing. The lessons learned, transformative.

Let's keep moving out into this territory and keep blowing up brackish!

Stay curious. Stay creative. Stay observant. Stay passionate...

And Stay Wet.


Scott Fellman

Tannin Aquatics 

Scott Fellman
Scott Fellman


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