Walstad Method Tanks: A Definitive Guide

walstad method tanks
Table of Contents

What is the Walstad Method?

The Walstad Method is a fish tank maintenance routine that is self-sustaining, created by Diana Walstad. It uses a combination of plants, fish, and snails to keep the tank clean. The routine is designed to replicate a natural ecosystem, rather than the more common fish-only tanks, and is intended to keep the tank clean and the inhabitants happy.

By creating a natural ecosystem, the idea is that you do not have to do water changes. How is this possible?

In nature, fish habitats have huge water volumes and large plant mass. On the contrary, the number of fishes and living things in the water is much lesser in nature. The ratio of water to plant mass to livestock is skewed highly that you do not need to conduct water changes.

I mean, water changes don’t occur in nature. In her book, Ecology of the Planted Aquarium, Diana Walstad theorised that by following nature’s methodology in aquaria, it is possible to create a self-sustaining aquarium where water changes are unnecessary.

Sounds interesting isn’t it? 

How does the Walstad Method work?

The Walstad method works because it is an approach that uses a large plant mass with extremely low bioload. One of those principles is that a stable aquarium ecosystem is capable of regulating its own biological processes, such as nutrient cycling and waste removal, and that these processes can be supported by the addition of organic matter through your livestock’s wastes.

By letting your aquarium ecosystem balance itself, you are effectively eliminating the need for water changes because everything is in balance.

In layman terms, the beneficial bacteria will breakdown ammonia and nitrite from your fishes’ wastes. The large number of plants that you use in your aquarium will then absorb ammonia, nitrite, and nitrate – substances that are detrimental to them. 

With only 1 or a few fishes, you allow your aquarium to regulate itself by finding a balance. Your beneficial bacteria provide nutrients for your plants, your plants absorb harmful substances for your fish, and your fish provides “food” for the beneficial bacteria. Thus, making it a self-supporting cycle.

Things Needed for a Walstad Aquarium

Well if you’re convinced that her methods work (it works, she did it in her book), and would like to try it out for yourself, these are the things that Diana Walstad mentioned you’ll need to replicate her methods.

An Aquarium!

If it’s not obvious enough, you’ll need an aquarium to start off with. As nature consists of large volumes of water, it’s best to choose an aquarium size that has a decent size. For a Walstad aquarium, I would personally go for a 60cm (2ft) tank minimum.

This gives me more room for errors should any mistakes happen. Honestly if it’s your first time trying this out, go for the biggest tank size you can. Bigger volumes of water dilute the toxicity of any potential mishaps that might happen. Your fish will thank you for this.

Plant Soil for Walstad Method

In her book, Diana recommended the use of the Miracle Grow Organic Choice Potting Mix. However, you don’t have to use the potting soil recommended by her. 

The reason this soil was recommended is due to its organic nature. Meaning, your choice of suitable soils will have to be 100% organic and there should be no chemical fertilisers added.

What’s been tried and tested by many aquarists is the use of topsoil. It’s important to understand that the topsoil you see in your garden centres or supermarkets may not be what natural topsoil is as defined in science. 

Natural topsoil contains mainly minerals and very little organic matter. You’d want to look for these types of topsoils.

Get enough soil to fill up about 3-4cm (1-1.5 inches) depth in your aquarium. Take note this amount depends on how much you’ll want to mix with red clay.

Red Clay

It’s recommended to mix red clay into your soil if you’re doing the Walstad method. Red clay is high CEC (Cation Exchange Capacity) in nature and will benefit your aquarium greatly.

To keep things simple, red clay will absorb the nutrients released by the soil you’re using. Because normal soil is more potent than aquarium soils, it will release nutrients faster. Having red clay mixed in with your soil stores the nutrients for a longer period so that you don’t have to change out the soil frequently and worry about excess nutrients leeching into your water column.

Not only that, red clay prevents anaerobic conditions in your soil. Anaerobic conditions occur when there’s not enough oxygen in your substrate. You’d want to avoid anaerobic conditions as they’re known to kill everything in your tank.

Lastly, red clay contains iron that’s beneficial for your plants. 

Do note that you should be looking for unfired red clay. Fired red clay has different properties than unfired ones and is not useful in the Walstad aquarium.

Continue reading to determine the amount you’ll need.

Preparing Your Planted Tank Soil

Before you even begin setting up your aquarium, you’ll need to prepare your soil first. Simply dumping everything into your tank without following these steps will cause a nightmare. Trust me, been there.


The first thing you’d want to do is to use a colander and sieve out large chunks of materials from the soil. If you see any form of bark or wood, remove it as it will float up in the water column even with a soil cap. You only want the soil for the Walstad method.

After you’re done sieving, a recommended mix of 50:50 soil and red clay is recommended by Michael, although a lesser percentage of red clay is fine too. 


Once you’ve got everything mixed, you’ll need to mineralise the soil you’re using.

What’s mineralising? 

Mineralising soil means preparing it for aquarium usage. Mineralising speeds up the decay of organics into humus. Humus is extremely stable and will not release ammonia into your aquariums. This also reduces the chances of anaerobic conditions from occurring.

To mineralise your soil, soak the mixture in a pail for about a week, making sure to change the water every few days. Stir up the soil when doing water changes and remove any floating particles you notice.

Soil Cap

A soil cap is basically a layer of sand or gravel that is used to prevent your soil from mixing into the water column. This ensures that any floating particles that are too fine remain in the soil layer and don’t cause problems.

A soil cap also prevents excess nutrients from leeching into your aquarium. This stops algae outbreaks from occurring.

Look for inert sand of any colour of your preference. Grab enough bags of them to make sure that you have about 3cm (1 inch) thick layer above your soil base. 

In total, your soil + clay layer should be about 3-4cm (1-1.5 inches) and 3cm (1 inch) layer of sand. If you’ve done everything right, this should be sufficient to keep the soil layer properly capped while giving enough room for plant roots to grow in.


If you’re doing a Walstad method tank, you’ll probably need fast-growing plants. Thus, good lighting is needed for you to encourage plant growth. 

It doesn’t matter if it’s a T8, T5, or an LED. Your lighting just has to be strong enough for your aquatic plants. Therefore, look for full-spectrum lighting that is specifically made for plants.

Otherwise, natural light can be good enough. 

Filters for Walstad Aquarium

This can be pretty controversial, but I’ve kept Walstad setups without filters. Now before you start hammering me in the comments, hear my justification.

A fish tank filter is supposed to help keep the water column clean through mechanical and biological filtration. Mechanical filtration merely keeps the aquarium looking clear. Thus, if we just look at biological filtration, a Walstad method tank is supposed to be able to do it.

Think about it, a thick layer of soil substrate, a layer of gravel or sand, and a large plant mass. You provide a huge surface for beneficial bacteria to grow while keeping a light fish load. 

I tested my water every other week and found that my water parameters were stable. I believed that if my water quality was good, it shouldn’t matter. However, the only trade-off was that I could see detritus on the surfaces of the setup. Something you should consider if you were thinking of going filterless.

I kept bettas that setup. They breathe atmospheric air so I wasn’t too concerned about the oxygen levels. However, you might want to reconsider if you’re keeping other fishes as water movement is essential for proper water oxygenation.

I would imagine if there’s a big plant mass, there should be enough oxygen for a low bioload, but that’s a risk you’d have to take.

Of course, you could just put in an air stone for surface agitation, but it’ll be more beneficial to get a filter instead. 

Depending on your tank size, I would recommend a hang on the back filter or a simple sponge filter. Larger tanks will require a canister filter for proper water circulation. 

Plants for Walstad Aquarium

In general, fast-growing plants are highly recommended, especially in the initial stages. This ensures that excessive nutrients are consumed, preventing algae growth. A good start would be to look for stem plants.

Stem plants are generally known to grow quickly in aquariums as they can take nutrients from both the aquarium substrate and the water column. Stem plants can also propagate extremely quickly. 

Cutting and replanting of the stem not only gives you 2 plants, but the stem of which you made the initial cut will grow into 2 stems (think a 2-pronged trident). This gives you more plants that will absorb more nutrients.

Imagine trimming these 2 “new” stems. More will grow and it will quickly take over your aquarium!

Almost any type of stem plant will do well in your Walstad tank. Depending on your previous equipment, make sure that the plant can survive in your aquarium! If you’re not injecting CO2 or do not have the strongest lights, low-demand plants can be used as well.

Another type of plant to go after are plants that grow from a crown. Unlike stem plants, these plants mostly propagate through sending out runners. 

Do note that not all crown plants are fast-growing and easy to take care of. Cryptocoryne species are pretty fussy of the water conditions and are slow growers. A recommendation would be to look for Amazon swords or any Echinodorus species.

Lastly, floating plants are your best friend! They are the faster growers that will suck up the extra nutrients in your aquarium fast. 

As they have access to atmospheric air, they are not carbon-limited and will help you out-compete algae.

Oh yes, apart from aquatic plants, riparian plants can help as well. Here are some riparium plants that you can use above your fish tanks.

Livestock for a Walstad Aquarium

Bettas! I personally love putting bettas – domestic or wild type bettas in Walstad setups. Firstly, as the soil substrate is mostly organic soil, the water conditions will slowly become acidic over time due to the decomposition that occurs. 

Soft water is great for bettas as they’re a soft water species. 

In fact, almost any soft water fishes or fishes that prefer lower pH are good for Walstad setups. Otherwise, go for hardier fishes that can survive in a range of water conditions.

Some good livestock for Walstad tanks are 

  • Bettas
  • Guppies
  • Mollies
  • Swordtails
  • Tetras
  • Danios
  • Snails (Malaysian Trumpet Snails are great for aerating the substrate while clearing up leftover fish food!)
  • Shrimps

Just ensure there’s enough oxygen for them and remember to keep a light bioload. 

Fishes to avoid for a Walstad Aquarium

Generally, you’d want to avoid cories, plecos, or other fishes that will disturb your substrate. As these fishes will dig, you risk exposing your soil substrate to the water column. Doing so will cause algae growth, and that’s something you’d definitely want to avoid.

Feeding your fish in a Walstad Aquarium

Even though the goal of a Walstad tank is to be self-sustaining, that doesn’t mean you don’t feed your fish! Although I would love to hear if you manage to achieve that through sufficient algae growth, a large shrimp colony, and just 1-2 fishes!

Your fish can survive days without food, so don’t worry if you don’t feed them. What I would recommend is light feeding every few days. This keeps the fish waste low, giving enough time for your biological bacteria and plants to do their jobs.

Setbacks of the Walstad Aquarium

It may sound like an interesting concept, but I wouldn’t recommend doing a Walstad aquarium if you’re a beginner. There are many things that might go wrong and you might not know what factors are causing it.

For example, if there’s an algae outbreak, what’s causing the issue? Is it because of a nutrient issue or due to bright lights? Could it be a lack of water movement?

Also, this method requires constant testing of your water parameters. As you probably won’t do much water changes, anything can go wrong. A test kit will be handy to tell you if need to do so.

There’s another issue of water evaporation. When water evaporates, pure H2O leaves the tank. This leaves behind other minerals that will make your water harder over time that your livestock might not like.

Unlike regular tanks where water changes will remove these minerals, you’ll need to use reverse osmosis (RO) water or distilled water to make these top-ups. Unless you already have an in-built RO unit at home, doing top-ups will be more expensive than your usual aquariums.


Yes, this is a pretty long post. But it’s necessary to really cover the different aspects of a Walstad method tank. If you think about it, the setup cost for these tanks is lower than your usual aquariums. You save on commercial aquarium soils, can get away with cheaper filters & media, use less fish food & water conditioners, and many more.

However, the long-term costs involved will stack up quickly. The regular water testing (test kits can get pretty expensive), water top-ups, and risks involved are certainly out of reach for beginner aquarists. Unless you have the budget and experience to do so, a Walstad method tank is definitely not for you! 

I hope this post was informational to give you a complete understanding of Walstad method tanks. If you have any questions or anything to contribute, do reach out to me!

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