The Walstad Method for Planted Tanks: A Complete Guide

Once you’ve kept a few aquariums you often begin to itch for something a bit different. Maybe you decide to try saltwater tanks for a while. Or perhaps Discus fish catch your interest. But what about trying something really different?

This guide is all about the Walstad Method, an aquarium that uses actual soil for growing plants and filtering the water for fish! Once established you can get lush plant growth with minimal inputs and next to no work besides feeding your fish and topping off the tank!

Intrigued yet?

What is the Walstad Method?

The Walstad Method was designed and popularized by Diana Walstad, North Carolinian biologist and aquarist. She set out to find a way to design aquatic indoor ecosystems that worked in harmony to provide for plant and fish health just as natural ecosystems do.

In the vast majority of aquariums we use filters, water changes, chemicals, filter media, carbon dioxide, fertilizers, micronutrients, and a host of other agents. These help balance out the fact that even the most spacious aquarium is vastly overcrowded compared to your local pond.

But what if we could do away with all of these additives? What if we could stick to water changes – or even just topping off the aquarium and letting the fish and plants be?

The Walstad Method is about making aquariums as maintenance-free as possible while still maintaining an ecosystem with healthy fish and plants. Let’s talk about how to set up an aquarium using the Walstad Method!

Essential Equipment for the Walstad Method

Here is a list of the equipment that you’ll need to set up a planted tank using the Walstad method.

Lighting

Using the Walstad Method there is a definite emphasis on using as little extra technology as possible. But there are a few things we simply can’t do without and full spectrum plant lighting is one of them.

In this aquascape we need healthy and abundant live plants because they provide filtration for the fish. Therefore we need lighting that will fuel photosynthesis, the process by which plants create sugar using carbon dioxide and water.

You may already have some bright lights. But if they are stock lights that came included with your tank, chances are they won’t be suitable. Aquarium plants need lighting with good to great photosynthetically active radiation (PAR) levels. Typical incandescent or fluorescent light fixtures don’t create light in the spectrum that’s photosynthetically active and is therefore useless.

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One great thing about the Walstad Method is that it can work in any size setup. Not only are Walstad aquariums popular but you can also use bowls or even jars full of soil and plants! So long as you provide the lighting and balance the needs of your fish and plants your creative possibilities are limitless!

Small to medium sized aquariums are especially popular with Walstad aquarists (10-40 gallons). This is most likely because Walstad tanks work really well with smaller community fish that don’t grow beyond 3 inches. Larger fish that need larger tanks are much more likely to disturb the plants.

However there’s no reason why you can’t go larger if so desired. The only real downside is that you’ll need higher powered lighting and your fish may get a bit lost! But you’ll have a tank rivaling that of any zoo once everything has fully grown in!

Plant Soil

Choosing your plant soil is just as important as your lighting when setting up a Walstad aquarium. Most soils will grow aquarium plants as well as terrestrial vegetables and flowers. But not all soils are good for aquarium use.

Many potting and vegetable soils have fertilizer additives, wetting agents, and other additives. These can fuel algae growth, shift the water chemistry, or simply take up space in the soil and are useless for aquatic plants.

We want to be using a soil that has a balance of organic and inorganic materials without it being too rich that it causes algae to explode. Organic potting soil is by far the best choice but always read the ingredients label on the bag.

If a soil is too rich in additives like chicken manure or guano it will need to be either reduced in volume, mixed with topsoil that’s free of nutrients, or avoided entirely. Other additives, like worm castings, are not nearly so rich.

There is a dizzying array of plant soils available in today’s market but don’t despair. Even if an ingredient that you’d rather not have is listed, you can likely make it work. For example, if a soil contains perlite, which is unnecessary, it will either float out of the substrate or be held down under your sand cap.

If a soil is too rich and you start to have runaway algae, reduce your lighting period and do water changes to remove free floating nutrients. Adding floating, fast growing plants like Hornwort or Duckweed will also add competition.

Mixing a rich soil with standard topsoil will also help cut down on it’s algae growing potential. You can use topsoil from a home and garden store or even topsoil from outside so long as you’re reasonably certain it’s not contaminated by fertilizers, pollution, etc.

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The best potting soil has organic matter plus bulk like peat or sphagnum moss and coconut fiber added. These agents don’t contain fertilizer but they do slow release plant tannins into the water. This slow flow of tannins helps to buffer even hard tap water towards neutrality, an ideal range for fish and plants.

Organic additives like feather and bone meal slow release calcium and nitrogen into the substrate right where plants need them most.

Filters, Heaters, and More

This is the best part about the Walstad Method! Besides lighting, plants, and soil, the rest of these are entirely optional! A heater is recommended if you intend on keeping warm water tropical fish like Gouramis and Angelfish.

However, many popular community fish do just fine in cold water aquariums as do many aquarium plants. Zebra Danios, Guppies, and Goldfish can all thrive in a heaterless tank alongside Pygmy Sword Plants and Vallisneria.

Filters are a tricky subject, however. Once the aquarium matures there is no real need for a filter unless you simply feel uncomfortable keeping fish without one. The plants and substrate provide a massive, living biological filter that’s running at prime efficiency.

Adding a filter won’t harm things and it provides a little extra space for denitrifying bacteria to take hold. However I would avoid using activated carbon in a Walstad tank. Activated carbon (charcoal) pulls out organic matter from the water column. While this includes free floating proteins and other unwanted agents, these molecules also feed good bacteria and helps sustain the ecosystem.

If the flow rate of your filter is too high, it will also tend to remove carbon dioxide from the water. Powerheads, airstones (bubblers), and filter outflow all add oxygen to the water, which is great for fish! But aeration isn’t so great for plants, which need carbon dioxide.

Carbon dioxide is always in short supply in a Walstad tank. Since we aren’t adding any CO2 we have to conserve what naturally dissolves from the air and more importantly, what bacteria release from the soil via decomposition.

Stirring the water column outgases what little is available, stalling out plant growth. It’s much better to simply keep a light fish load and fill the tank with plants to meet their oxygen needs in a Walstad aquarium!

Preparing Your Planted Tank Soil

Once you have your supplies, there are a few things to consider when setting up a Walstad tank. The first is how to add the planting soil you’ve chosen.

You will need to screen out large chunks of matter like twigs, leaf fragments, perlite, and other useless debris. Otherwise they will simply take up space in your soil bed or float off into the water column.

Run the soil over a colander or piece of window screening to isolate these components. Once you have your sifted soil, you can add it directly to your aquarium, bowl, or jar. But don’t fill the container all of the way. Otherwise, you will be looking at a mess of muddy water!

Instead, we need to add just enough water that the potting soil is thoroughly wet to the point of being a thick mud. At this point, we need to add a capping substrate to keep the soil from mixing into the water column!

The two most popular choices are gravel and sand for this layer. Both have their advantages for growing plants. I personally prefer sand because it’s easier for smaller plants to root in however gravel is just as usable.

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The cap layer should be ¾-1 inch thick if using sand and 1-2 inches thick if using gravel. Any of the planting substrates I’ve listed here will work wonderfully in combination with a soil layer.

I prefer either Black Diamond Blasting Sand for its look or a clay-based substrate like Seachem Flourite. Clay substrates not only look good but have the ability to bind free-floating nutrients, boosting plant growth even further!

Sand substrates are also wonderful playgrounds for burrowing animals like Kuhli Loaches and aquarium snails. In gravel aquariums we don’t get to see these natural habits. With a sand and soil substrate they not only root about for food but actively aerate the soil, keeping it from going anaerobic (toxic) and helping plant roots thrive.

Soil Additives

Many Walstad enthusiasts insist on sticking to potting soil and sand or gravel. Others prefer enriching the substrate even further while it is still exposed. Like terrestria gardening opinions vary and there is no real right way.

Some popular additives include adding crushed coral to raise the pH in soft water regions and mineral powders that provide inorganic nutrients like calcium and potassium. Osmocote consists of small granules of slow-release fertilizer that can be used in the soil to further enrich it without causing an algae explosion.

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Many, if not most, of the potting soils you’ll find already have some enrichment, though. After all, the plants still need nutrients to survive. Bone meal, worm castings, and other organic additives are all you really need. I recommend experimenting over time and seeing which combinations of soil, substrate cap, and additives work best for you!

Plants for a Walstad Method Aquarium

Choosing the right plants for the Walstad Method is extremely important as well. Unfortunately, many of the aquarium plants that get displayed in showy aquascapes simply won’t work in a Walstad. These include plants with high lighting and CO2 demands like Dwarf Baby Tears and other carpeting plants.

We need fast growth yet the plants need to be able to grow without too many inputs from us. It’s a challenging problem but one that Diana has worked out through years of careful testing!

In her (and my) experience, aggressive root feeders with low to moderate light demands work best in a Walstad aquarium. Floating plants are fantastic because they sit right near the light and can get abundant CO2 from the air. Plants with large lily pad-like leaves also thrive for the same reasons.

Good Floating Plants for the Walstad Method:

  • Red Root Floater
  • Hornwort
  • Cabomba (free floating)
  • Water Lettuce
  • Dwarf Tiger Lotus
  • Duckweed
  • Salvinia
  • Banana Plant

Floating plants are a great way to control algae growth because they create shade underneath themselves. They also tend to grow very quickly, sucking up vital nutrients that algae would normally be using. Just be careful not to let them completely dominate your subsurface plants – this is why starting with fast growing submerged plants is just as important.

Good Fast Growing Plants for the Walstad Method:

  • Hornwort (rooted)
  • Ambulia (Limnophila sessiliflora)
  • Anacharis (Elodea densa)
  • Hygrophila sp.
  • Vallisneria sp.
  • Sagittaria sp.
  • Sword Plants (Echinodorus sp.)
  • Brazilian Pennywort (Hydrocotyle leucocephala)

Once your ecosystem is mature and you have enough fast growing plants to handle excess nutrients you can start thinking about adding slower growing plants that you enjoy. This list is considerably larger than what I have listed. You just don’t want to start with these plants because they won’t grow fast enough to help jumpstart the ecosystem.

Good Slow Growing Plants for the Walstad Method:

  • Cryptocoryne sp.
  • Anubias sp.
  • Java Fern
  • African Water Fern
  • Mosses
  • Ludwigia sp.
  • Monte Carlo (Micranthemum tweediei)
  • Creeping Jenny (Lysimachia nummularia)

Since our plants are our filter we want as many of them as possible as quickly as possible! Ideally, 70% of the surface of the substrate should be covered by plants. Less can be okay but keep in mind that this is unused filtration capacity that makes it harder for the ecosystem to stay in balance.

Aquascaping in a Walstad Method Aquarium

You can aquascape a Walstad aquarium as you would most planted tanks. However there are a few things to keep in mind. Since we have a layer of biologically active soil, we need to make sure that there are plenty of plants taking advantage of it. As stated earlier we want around 70% of the surface covered in plants.

Diana also recommends against using large rocks and driftwood chunks in Walstad tanks. They sit on top of the substrate and prevent plants from taking hold. They also compact the substrate and prevent water from flowing freely – this can cause the soil to go anaerobic.

Thick anaerobic patches can be a real problem. Anaerobic means “without oxygen.” The bacteria that live in these conditions create toxic fumes like hydrogen sulfide, which is poisonous to all aerobic organisms like animals and plants.

That said, small rocks and pieces of driftwood aren’t a problem. Just don’t allow them to take up too much planting space and you’ll be fine!

The Jungle aquascape is by far the best aquascaping style for a Walstad tank. Basically, we let the plants grow into one another just like you’d see in nature. No regular rows or tidy little groups. Just plants forming a chaotic thicket.

What I like about the Jungle look is just how hands-off it is. Once your plants are put into place, you simply sit back and let nature do the work. It’s perfectly in line with the theme of a Walstad tank. 

The plants will compete and balance each other, threading in and around each other in ways you wouldn’t be able to do intentionally. As a result, mature Jungle tanks look absolutely incredible, as if you took a slice out of a lake and set it into your room.

Cycling a Walstad Method Aquarium

Cycling a Walstad aquarium can be a little tricky because it’s so different from a typical, filter-using tank. In her book “Ecology of the Planted Aquarium,” Diana actually recommends adding fish right away along with the plants!

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The theory is that the soil already contains loads of bacteria capable of breaking down fish waste, which is true. Walstad aquariums therefore don’t usually suffer from New Tank Syndrome.  

Fish and invertebrates also provide valuable nutrients through their waste, consume and break down plant debris, and add valuable carbon dioxide to the water column. If plants are the filter for your fish, the animals are filters for your plants!

On the other hand, there is a chance that something can go very wrong if this is your first Walstad. A soil too rich in nutrients may leech ammonia directly into the water column. Ammonia is a vital plant nutrient but deadly toxic to fish. If you don’t have enough plants to uptake it you can easily kill your newcomers. 

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I personally recommend a middle approach: stocking lightly immediately as you would a typical aquarium. After 1-2 weeks, if your water tests show no sudden increases in ammonia or nitrate and the pH seems stable, then stock the tank as you would any other aquarium!

The cycling stage is the one period where I would recommend using chemical additives if needed. Ammonia reducers like Kordon Amquel can detoxify ammonia instantly, saving your fish if you get a reading that’s too high.

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Fish for the Walstad Method Aquarium

Lastly, we need to think carefully on what fish to add when creating a Walstad aquarium. Seeing as we’re replicating what exists in nature, technically any fish would work here! However the ecosystem is so much smaller that we have to be a bit more thoughtful.

Disruptive fish that like to dig deeply or large burrowing fish are best avoided. Small diggers like Dwarf Cichlids and smaller Loaches aren’t a problem. They even help aerate the substrate for plants and keep worms and other aquatic organisms in check.

But larger Cichlids, Catfish, and Goldfish need to be chosen carefully. If you want to keep Goldfish in a Walstad, I recommend using a thick gravel substrate. This way they won’t disturb the bottom layer too much. Other digging fish like Cichlids may not work as they tend to dig deep breeding pits and uproot plants with gusto when spawning.

Fortunately, nearly all community fish work wonderfully in a Walstad so long as they aren’t strict vegetarians and thrive in the temperature range you’ve selected. 

Good Fish for a Walstad Aquarium:

  • Bettas and Gouramis
  • Tetras, Livebearers, small Barbs, Danios, Otocinclus, and other Community fish
  • Goldfish (with consideration for the substrate)
  • Kuhli Loaches, Dwarf Cichlids, Corydoras, and other small digging fish
  • Hatchetfish, African Butterfly Fish, and other Surface Dwelling fish
  • Invertebrates (Snails, Shrimp, Dwarf Crabs, Dwarf Crayfish)

Conclusion

Walstad aquariums offer something very different from your typical tank using a sterile gravel substrate. Potting soil provides nearly everything aquarium plants need and fish can provide the rest. Meanwhile, the fish thrive due to the activity of the plants. 

These aquariums are a living example of interconnectedness. And best of all the system is extremely low maintenance! In fact the less you mess with it, the better, just as in nature!

I highly recommend everyone try setting up a Walstad jar, bowl, or tank at least once. After you see just how much your plants thrive and how easy they are to maintain, I’m sure a second, third, or fourth setup will be in your near future!

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