If you want to join the ranks of the 7.2 million American households that maintain aquariums, you’re making an awesome choice! Fish are a fairly easy pet to care for, and it’s really rewarding to take care of an environment and watch the inhabitants that dwell in it thrive.
A blackwater aquarium is one of the best ways to ensure that your aquatic life flourishes as much as possible. Here, we’re going to talk about what this means and why you should consider a blackwater aquarium. Read on to learn their many benefits and how you can start setting one up!
What is a blackwater aquarium?
When you think of an aquarium, you likely think of a bright, colorful space where you can watch your multi-hued fish swim among beautiful plants and rocks. However, this may not be the best environment for some species of fish to thrive. A blackwater aquarium is an alternative to these brightly-lit spaces that can be stressful for fish.
This biotype is most commonly associated with South American fish. And if creating as natural of an environment for them as possible is your goal, then blackwater is it.
Whether in the Amazon river basins, its tributaries, or the floodplains, you’re not likely to find pristine-looking waters like you would in a home aquarium.
You’re far more likely to find dark tea-colored water teaming with tannins from driftwood and decaying plant matter.
Since this is the native environment for a lot of fish, why not try to replicate that at home?
A blackwater aquarium sets out to mimic their environment as much as possible.
- Soft, acidic water ranging from a light tea color to a dark brown water column
- Generally planted with low light plants and floating plants
- Lots of driftwood
- Usually a fine gravel or sand substrate
- Rocks, twigs, and leaf litter will add to the natural aesthetics
Benefits of this biotype
At this point, there’s likely one question floating around your mind: why? Why would anyone choose to create an environment that looks dirty and doesn’t brightly show off your fish?
We brushed upon this earlier, but the main answer is that it may be better for your fish.
The darkness of your aquarium is created by leaving natural driftwood, dark leaves, and debris in your aquarium. This is what makes pond and lake water dark.
You’re essentially simulating the natural habitat of the fish who live in your aquarium, and the tannins that occur naturally in plants just happen to darken the water. Think of dark water as a symptom of having a natural environment rather than the ultimate goal!
Additionally, the pH of these aquariums is generally lower, making the water more acidic. There also is less sodium, magnesium, potassium, and calcium concentrations within the tank.
Since these fish naturally thrive in bodies of water that are more acidic, this is a great way to keep your aquarium pets healthy and thriving.
Health benefits of blackwater
Yes! There are actually scientifically proven health benefits for fish living in this environment. Scientists have determined that the humic substances, found within decaying plant matter, can have a direct effect on health.
Humic substances are comprised of humis, humic acid, and fulvic acid.
Studies have shown that humic substances have multiple benefits:
- Better absorption of eaten food
- Higher and healthier yields of eggs and fry
- Natural resistance to fungal and parasitic infections
- Faster healing after infection or injury
- Increased vitality and lifespan
Understanding tannins and humic substances
Tannin is a general, and often times over-arching, term used to describe any discoloring of your aquariums water. However, this isn’t always the case.
The main difference is that tannins reside within plant matter such as wood, nuts, cones, and leaves, while humic substances are present during the decay of these organisms.
Both can be responsible for the tea coloration of your tanks water independently of each other.
Tannins will leech out of driftwood and leaf litter, however, humic substances will also be present. With that said, it is possible to have humic substances without having any tannins, such as tannic acid, with the same coloration result.
The health benefits are from humic substances, not tannins.
It’s also worth noting that humic acid is a dark brown color while fulvic acid is more of a yellow. All, including tannins, can be concentrated within your aquarium to produce a color range of slight yellowing to a very dark brown.
There does not appear to be any negative effects on fish at any concentration.
Maintaining a blackwater aquarium
Just like with any other aquarium set-up, a blackwater aquarium will require general maintenance. However, it won’t be any more maintenance than what you’re probably used to.
The only key difference with this set-up, versus a traditional set-up, is with the material you will use that produces the tea color you’re looking for.
The best tannin producing material
Not all organic material is created equal so be sure to know what you’re adding to your tank. Here is a list of the best tannin producing material that I recommend and use myself.
- Driftwood – Any driftwood that is safe to use will do. However, some produce more tannins than others, such as:
- Mopani
- Malaysian
- Cones such as Alder and Birch
- Various seed pods
- Bark, sticks, or twigs from any of the “safe to use” woods
- Leaf litter
- Indian almond leaf is the most common
- Malaysian mangrove or mulberry leaves
- Catappa leaves
- Peat
- Commercial conditioners that contain humic material
While commercially available blackwater conditioners are out there, they only serve to condition the water. They will not give you the “look” of a blackwater biotope other than the color.
You can’t replace the natural look of wood and leaf litter with a bottle.
Controlling how dark your aquarium is
Now that you have the important ingredients for a thriving blackwater aquarium, it’s time to control the color.
A lot of this is completely up to personal preference. Your aquarium’s water can range from a slight yellowing of your water to a deep brown color.
The easiest way to darken your water is to either add more tannin producing material or to add in some “tank tea”. This can be a commercial conditioner (mentioned above) or homemade (details below).
To lighten the color simply remove or lessen the tannin-producing material and allow it to slowly lighten with water changes.
If you’re looking for something a bit more drastic you can add carbon to your filter or filter floss.
As with any self-contained living environment though, it’s best to make slow and small changes. This will allow your aquatic friends to adjust.
How often to replace leaf litter
This is where the actual maintenance comes into play. No, you shouldn’t just leave leaves to deteriorate into your substrate.
Like with any organic material, it will break down over time and need to be replaced. This is at a minimum. Don’t allow your leaf litter to rot.
However, since we are also enjoying the benefits of the tannins that it produces, as well as the humic substances, changing them out more often will be required.
All material will eventually stop leeching tannins in any noticeable amount. If the leaves are in good condition still, feel free to just add more. Personally, this is when I swap them out for new leaf litter.
Swap out half your leaves at a time. Or less if you can. The point is to avoid swapping out your entire leaf litter in one shot.
You can expect your leaves to last at least 30-60 days. This timeframe can vary depending on your set-up. The more current in your tank and the more fish that can either feed off of or disturb the leaves, the shorter the time frame.
Blackwater effects on PH
The main point, when it comes to PH, is that fish that would thrive in a blackwater biotope prefer acidic water. This is anything below a PH of 7.0.
The great thing about all the different organic materials that I’ve talked about so far, is they will not raise your PH. The lowering effects, however, pertain to soft water.
The common belief is that any driftwood or organic material will lower your PH. This isn’t always the case though. While acids such as humic, fulvic, and tannic are capable of lowering your PH the conditions must be right.
In water with high alkalinity, for example, you’ll have a hard time lowering the PH without directly adding acids. I don’t recommend this at all.
Another factor is your water’s hardness. Water with high KH, or carbonate hardness, will also be very difficult to lower the PH in. The carbonates act as a buffer that will neutralize the acid.
It’s important to know what the PH of your tap water is. If your tap water is generally alkaline, a blackwater biotope may not be the best option for you without the use of RO water.
Make your own tank tea concentrate
Why buy from a store what you can easily make at home, right? While there is certainly a convenience factor to buying a premade blackwater conditioner, making your own at home isn’t that difficult.
The other plus to making you own is that you can control exactly what goes into it without any added chemicals. Oh yeah, and it’s cheaper.
There are a couple of ways to do this. The first way is slower and not concentrated. You’ll set aside another tank or large container and soak all the tannin producing material you wish. When the water is nice and dark, simply include some of that water in during your regular water changes.
To make a concentrate you’ll want to soak the material in a bucket to ensure it’s all waterlogged. After a couple of days, you want to boil the water with the material in it. This will ensure most of the tannins are released and into the water.
After it cools, strain out the material leaving only the tannin laden water.
To concentrate it even more you can again boil the water. The water will evaporate off concentrating the tea even further.
This can now be stored in much smaller containers giving you better control over how much is being added to your tank.
Best plants for blackwater aquariums
A blackwater aquarium doesn’t have to have live plants. There are many that mimic the faster-flowing waters of this biotope where plants would be scarce anyway.
However, if live plants are preferred, this can easily be accomplished.
Since your aquarium will be darker than a traditional set-up, you’ll want to go for plants that do well in low light conditions. Also, any floating plants will limit the amount of light that will reach the rest of the tank.
Some good floating plants that I recommend are:
- Red Root Floater
- Water Spangles
- Water Lettuce
- Frogbit
For non-floating plants you’ll want to go with low-medium light, easy to care for plants. I prefer plants that have rhizomes and get their nutrients from the water column.
Here are the plants that I recommend and work well in blackwater:
- Anubias (all species of Anubias are safe)
- Bucephalandra (most species of Buce will work)
- Cryptocoryne (low light species only and not all have rhizomes)
- Java Ferns (all species would work)
- Java Moss (will work better than Christmas moss)
Lighting, Heating, and Filtration
A blackwater aquarium’s requirements are pretty much the same as any other freshwater aquarium set-up. There are subtle differences though. Aquarium lighting can be confusing but don’t overcomplicate it.
Lighting
Since a blackwater set-up typically requires less light than a normal planted tank, you can save some money in this category. Light only serves two purposes; to illuminate your fish for viewing and to aid in photosynthesis in plants.
However, since you’ll be using low light plants anyways, there’s no need to go crazy here. There are plenty of affordable LED lights on the market. With that said, if you do decide to go with plants you’ll likely need one step up from the cheap lights aquariums come with.
Heating
Blackwater set-ups will typically be in warmer climates with tropical fish. This will require you to keep the water heated. I personally keep mine at 78 degrees, but anywhere between 75 and 82 would be just fine.
Since that’s a little warm for most people’s houses, you’ll want to use a heater. If you’re lucky enough to have a fish room you can simply heat the entire room.
Here’s an article all about aquarium heating.
Filtration
Aquarium filtration is done by mechanical, biological, and chemical means. Let’s break each one down for its uses with blackwater aquariums.
Mechanical
Mechanical is what catches and collects any debris that your filter sucks up. This is usually done with the use of foam or pads. Since a blackwater aquarium will have more debris than a typical set-up, you’ll want to keep this from getting clogged.
It’s not only good for collecting fish poop and uneaten food. It’s also great at collecting the small bits of your leaf litter as it begins to break down. Just don’t allow it to rot because it will spike your nitrates and can poison your fish.
Biological
This is a given. All aquariums must have beneficial bacteria that converts ammonia to nitrites to nitrates. This doesn’t change with this set-up.
Chemical
There are really only a couple of reasons to ever use chemical filtration. One is to remove medication after treating your tank from an illness. And the other is to clarify your water.
But wait… Won’t that also remove my tannins? Yep, it sure will.
There really isn’t any need to use this type of filtration in a blackwater aquarium. The only exception is for intermittent use to lessen the amount of tannins present. Water changes will do the same thing though.
Blackwater Fish
Not all fish will thrive in this environment. It’s not the tannins or the humic substances that are the issue though. Since these set-ups will typically have lower PH, you probably won’t want to go with fish requiring alkaline water, eg., African cichlids.
Here are some good fish options that will do well in a blackwater environment:
- Discus
- Angelfish
- Tetras (most species)
- Plecos
- Hatchets
- Corydoras (most species)
- Rams (if PH isn’t too low)
- Apistogramma
- Barbs (some)
- Certain catfish such as the Raphael
- South American Cichlids (with caution)
While many South American cichlids will do well in this environment, some I’ve already listed above, caution should be used with the larger species.
Larger species of cichlids are known to dig around their tank. In a tank with leaf litter and plants, they can easily disturb everything and break down the leaf litter much faster. They will also limit you on what other fish you can have in your tank. The “large cichlid” exception is Discus.
There are many other fish that can put in a blackwater aquarium but these are the most common and easiest to keep. Common set-ups will typically be discus with tetras or angelfish with tetras. Corydoras do well with both. My personal favorite tetras for blackwater are Cardinals and the red and blue Colombians.
You’re now ready
Congrats, you are now fully prepared to dive into this beautiful and natural way to keep fish. You probably already have everything you need to get started. Except maybe the leaf litter, cones, and pods. Luckily those are easy to find online. Now all you’ll need to learn is how to answer all the questions you’ll get from those unfamiliar with blackwater aquariums.
