fish in blackwater aquarium

Blackwater Aquarium Guide: Blackwater Biotope

Blackwater aquariums are becoming more and more popular. They’re enchanting and beautiful if done right. However, the dark water and leaf litter can be challenging, especially for beginners. In this blackwater aquarium guide, we take the guesswork out of setting up a blackwater biotope and get straight to what you need! We’ll cover everything from water chemistry to tank selection to ideal fish species.

Whether it’s your first time setting up an aquarium or your tenth, this guide provides all of the information that you need in order to make educated decisions about your tank setup without having to do hours of research on your own. Let’s get started.

Recommended for your Blackwater Aquarium :

​​What is a blackwater aquarium?

Biotope aquariums are tanks modeled after natural ecosystems. If you’re trying to imagine what this looks like, think about jungle streams, rocky lake beds, or dense vegetation and slow-moving pond waters. You won’t find bubbling treasure chests and neon gravel here.

Blackwater aquariums are one type of biotope aquarium. They’re as challenging to keep as marine tanks but once you get them established, they can be very rewarding.

To give additional context around the name, the Amazon river can be classified as having both whitewater and blackwater areas.

As the name suggests, whitewater habitats tend to have relatively clear water. They also have a neutral pH around 7.0.

Similarly, blackwater habitats have dark-colored water. The color of the water is caused by large amounts of dissolved humic substances. If the river extends into a floodplain in the forest, the leaf litter, seeds, fruits, and woods from the forest will even get into the water and dissolve, tinting the water with tannins and other compounds.

Blackwater aquariums try to recreate the blackwater environments of the Amazon.

Why is the water so dark in a blackwater aquarium?

The water in a blackwater tank will be much darker than that of a whitewater aquarium. The logs, twigs, and leaves will begin to decay over time and release particles into the water. This will stain the water, with the color ranging from nearly black to a faint brown tint. Because dissolved organic materials tint the water, it is often described as tea-like. The water becomes a literal “soup†of all kinds of organic compounds.

The chemistry behind the water is complex. The most important idea here is that the color is driven by natural compounds, which also lower the pH as they’re released into the water.

How to Set Up a Blackwater Aquarium

It’s a matter of personal preference when it comes to aquascaping. No two tanks will be identical. However, we’ve outlined some basics below based on years of maintaining blackwater tanks.

Aquarium

Size is completely driven by your space and what you’re looking to build. You can start with a nano tank or you can build a massive, 100+ gallon tank! You can use a rectangular tank or a bow-front aquarium. As a general rule of thumb, larger tanks are easier to maintain consistent water conditions. But larger tanks are also more expensive. Here are some good tank options to get you started:

Substrate

If you have a planted tank, you have two options: fine gravel (not sand) or a specialty planted substrate like Flourite Dark. Both will anchor plants and provide a root zone.

Avoid marine sand or gravel, which is made of crushed aragonite and/or limestone. This material will dissolve in water and will make your pH and hardness too high.

Lighting

The blackwater biotope is naturally dimly lit. It has a jungle canopy above it that blocks and filters the light. This is the environment you’re trying to recreate.

We recommend choosing an LED light for your tank. White LEDs can mimic sunlight passing through the forest trees. If you can change the color spectrum on your lighting system, you can experiment with different colors to find the most beautiful mix. We love this Finnex Planted+ 24/7 HLC Aquarium LED Light.

Don’t try to skirt purchasing a good light. Aquarium plants need photosynthetically active radiation (PAR) from their lighting. Standard incandescent and fluorescent fixtures won’t cut it; they don’t have enough PAR. This issue is further compounded in blackwater tanks where less light passes through.

Carbon Dioxide

Carbon dioxide supplementation isn’t really needed in a blackwater aquarium. Plants in these environments tend to grow slowly so no need to include CO2.

Heater

Blackwater tanks typically run on the warmer side, from 75-80 degrees Farenheight so you’re going to want an aquarium heater. This model – Eheim Jager Aquarium Thermostat Heater – is a great choice.

Thermometer

Maintaining a consistent environment is important in a blackwater tank. Because you’re heating the water, we also recommend a thermometer so you can easily do temperature checks in the tank. Some models also have temperature controllers so you have automated control over your heater (and don’t cook your fish). Our aquarium thermometer guide covers options or you can cut to the chase and buy the best thermometer.

Water

Water parameters are an extremely important component of blackwater aquariums. You will need soft, acidic water. Tannins (from driftwood and Indian Almond Leaves) will naturally bring the pH down a bit, but getting the right water chemistry will require some effort on your part. The water should be low in hardness (GH) and alkalinity (KH). The ideal range is in the 2-5-degree range.

Matching the natural pH of blackwater rivers will be challenging, if not impossible, as pH can get as low as 4.5. Therefore, we are shooting for less than 7 for home aquariums.

Reverse osmosis water is a good way to achieve the correct parameters, especially if you have hard tap water. Blend the hard tap water with reverse osmosis water to get it where you need it. You’re not shooting for perfection; you just want the hardness to be less than 8 degrees. The softer water will help the pH drop over time.

Because there are so many elements going on with water parameters, we recommend stocking up on kits:

Water Flow

Blackwater biotopes naturally have moderate water flow. With a smaller aquarium, a HOB filter can likely provide enough water movement. For larger tanks, consider a canister filter to create sufficient water flow. You don’t want your tank to be too agitated though, as it can stress your fish and plants.

Filtration

Mechanical filter media can be used to capture debris that will naturally occur in blackwater tanks. Sponge filters are a great option and should be cleaned or replaced monthly to keep them functioning properly.

If your tank water is getting too dark, you can use activated carbon to remove humic substances. However, don’t go overboard here, or else you will strip the water too much. We recommend one week per month max.

Driftwood

Creating a blackwater biotope-type tank means mimicking river bottoms. Think logs, sticks, and wood. For the aquarium owner, this means you can use any kind of Driftwood that’s safe for aquariums.

But there is a twist for blackwater tanks – you don’t need to treat the wood first. Don’t want to boil the driftwood. By not boiling, the wood will release more tannins into the water.

Another awesome option is Manzanita wood. It has a neutral pH so it won’t alter your tank conditions.

Rocks

Most types of treated rock can be used safely in your blackwater aquarium. Avoid sharp or jagged edges to keep your fish safe.

By treating the rock, you will prevent the release of calcium, alkalinity, or microbes into the water which would negatively impact your water parameters. Also, avoid using rocks from a stream or river that you gather, as they can be known to introduce disease or other issues to your tank.

Leaf Litter

In the quest to make your water dark, leaves are your friends. We recommend using a variety of leaves, as they all have different decomposition rates. Recommended leaves and natural debris options include:

  • Indian almond
  • Alder cones
  • Red oak
  • Sessile oak
  • European beech
  • Hawthorn
  • Japanese maple

There is no scientific answer on “dosing†with leaves to get the desired water color. Almond leaves can be used at a rate of two leaves for 10-15 gallons. Over time, they will break down and need to be replaced. You can plan on replacing them every 30 to 60 days. If you’re using a mix of leaves, we recommend starting slowly and adding more leaves over time.

Best Plants for a Blackwater Aquarium

Plants aren’t a requirement in blackwater aquariums although they do add natural beauty to the tank and help support water conditions. If you choose to add live plants, select medium to low-light plants such as the following:

Additionally, we recommend using liquid plant fertilizers in blacklight tanks because of the lower light conditions. It helps to make sure the plants are flourishing, especially when the tank is just getting established.

Best Blackwater Aquarium Fish Species

We’ve been going through a lot of tank specifics. While the tank set-up is incredibly important, it is also fun to talk about potential fish species!

There are over 200 species of freshwater fish that inhabit blackwater environments in nature. Some species can grow quite large so you will need to plan for this when thinking through your tank. Here are some potential blackwater tank fish:

How to Adjust Water Parameters in a Blackwater Aquarium

There are three main ways to adjust water parameters in your tank:

  • Tannin & Humic Acid sources: Peat, Driftwood, Bottled tannins, Indian Almond Leaves, decaying plant matter
  • General Hardness (GH) reducing resins
  • Distilled or Reverse Osmosis (RO) water

Blackwater Conditioner

Blackwater extract is important to regular aquarium maintenance. Water changes will abruptly change the water conditions. Based on your tannin and humic acid sources, the previous parameters can be restored, but it will take time. Your leaves won’t start dumping their compounds just because you changed 25% of the water. And over time, sources like driftwood will become less effective and run out of compounds to leach. This is where Blackwater Conditioner comes into play.

Blackwater conditioners are generally highly concentrated so use sparingly and read directions carefully.

Indian Almond Leaves

Indian Almond leaves are a popular source of humic substances. They’re affordable and widely available. They’re also easy to use: just scatter a few on the tank surface. Over time, they will absorb enough water and sink to the bottom of the tank. Each leaf should last 30-60 days.

Our Pick
SunGrow Mini Catappa Indian Almond Leaves

What we like

  • They arrive relatively fresh
  • Most leaves were whole and unbroken
  • Their size makes them ideal for smaller tanks
Check Price on Amazon

They are pretty powerful so it is best to be slow in your application so you can see the full effect. However, when you see the water start to clear up, it is time to add more because the leaves have leached their tannins.

How many leaves do I need?

There is no official answer here, really. Generally speaking, almond leaves are dosed at two leaves for 10-15 gallons. However, they can be pretty powerful so we recommend starting slowly and adding over time.

Driftwood

Driftwood is a great source of plant tannins. It is huge relative to leaves which means it has a lot of tannins that will be slowly released over time (months to years), giving a consistent color to your tank. We recommend seeking our large, dark, dense pieces of wood, like Malaysian Driftwood and Mopani wood. Avoid Cholla wood.

Purchasing pet store driftwood is recommended over wild pieces of driftwood. We have heard horror stories of pollution, snails, leeches, parasites, you name it! Unless you are a tree expert and can confidently identify your wild driftwood and treat it properly (via boiling and/or extensive drying), just purchase the pet store version.

Maintaining the Blackwater Aquarium

There is no magic technique to maintaining a blackwater aquarium. Consistency and environmental stability are incredibly important for fish health so that is a priority over perfection in maintaining the ecosystem.

Weekly water exchanges are an important part of any aquarium maintenance regimen. We recommend somewhere between a 20-25% weekly change. With a botanical-influenced aquarium like a blackwater tank, you’ve got a lot of decaying biological material in addition to fish waste. You want to minimize the impact of any organics accumulating in a detrimental manner. 

Some fishkeepers keep their leaves and organic materials in the tank until they completely decompose. Other fishkeepers like to remove them for a “fresher” look. This decision is driven by aesthetics and is not a make-or-break water quality decision.

For more information about aquarium cleaning and water changes, check out our aquarium cleaning guide.

Blackwater Aquarium FAQs

Do Bettas like blackwater?

Yes, Bettas like blackwater environments. In the wild, their natural habitats are slow-moving waters like swamps, small creeks, and rice paddies. There is typically a good amount of sediment and organic debris in these environments, which turns the water a dark brown color.

Do shrimp like blackwater?

The answer really depends on the shrimp species. A lot of shrimp species come from rivers in Southeast Asia where there is a lot of organic debris in the water, creating natural blackwater environments. Ghost shrimp could likely adapt and do well in a blackwater tank, as could Crystal Shrimps and Tiger Shrimps.

Conclusion

Blackwater aquariums are becoming more popular with hobbyists and professionals alike. They’re a more challenging biotype so it is important to know how to set up the tank for success! We understand that blackwaters can be daunting when you first start out which is why we wanted to create this guide on the best tanks, filtration systems, lighting, and substrate for blackwater tanks. What kind of experience have you had with your blackwater aquariums? Tell us all about it in the comments!

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