Do We Really Need a Filter in a Natural Ecosystem Aquarium?

 When people talk about natural aquariums, the dream usually looks like this:

• Deep soil or sand

• Lots of plants

• Driftwood and leaves

• Very gentle movement

• Maybe… no filter at all

Then you go online and see “Walstad method”, “no filter tank”, “just plants and soil”.

It sounds nice:
Less equipment, less noise, more “nature”.

But then another side of the internet shouts:

“You must have a filter or all your fish will die!”

So which one is true?

In this post, I want to break it down in simple language:

• What a filter actually does

• Where beneficial bacteria really live

• When a filter is optional

• When a filter is your best friend

• How this connects to shrimp and natural ecosystem tanks

This is the next part of my water & basic system series, after talking about soft/hard water and GH/KH/TDS.

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1. What Does a Filter Actually Do?

Let’s strip away all the marketing and keep it very simple.

A filter usually has three main jobs:

1. Mechanical filtration

   • Catches physical dirt: poop, leftover food, plant bits

   • Like a net or sponge for particles

2. Biological filtration

   • Provides surface area for beneficial bacteria

   • These bacteria convert toxic ammonia → nitrite → nitrate

   • This is the most important job for long-term stability

3. Sometimes chemical filtration

   • Using activated carbon or special media

   • Removes certain dissolved substances (medications, odors, etc.)

Plus, a filter also:

• Moves the water around

• Helps oxygen reach all parts of the tank

• Avoids “dead zones” where waste just sits

So the heart of the story is actually:

“How do I support beneficial bacteria
and keep waste from building up too fast?”

A filter is just one tool that helps do that.

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2. Bacteria Don’t Only Live Inside the Filter

This is the part many beginners don’t realize.

The beneficial bacteria that run the nitrogen cycle don’t only live in the filter.

They live everywhere there is:

• Water

• Oxygen

• Surface

Which includes:

• Substrate / soil / sand

• Plant leaves and roots

• Driftwood and rocks

• Glass

• Decorations

• AND filter media, if you have a filter

So even if you remove the filter:

• Bacteria still exist in the tank

• The tank can still process ammonia → nitrite → nitrate

• Especially if there’s a lot of substrate and plants

That’s why some well-planted, low-stock tanks can survive without a traditional filter.

But.

Just because bacteria can live everywhere doesn’t mean every tank is ready to go filterless.

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3. When a Filter Is Optional

There are real-world situations where you might not need a traditional filter.

Usually, they look like this:

• Big volume, small bioload

  • For example: 60–100 L with only a few tiny fish or just shrimp

• Deep, mature substrate

  • Soil or sand that has been running for a long time

• Heavy planting

  • Fast-growing plants, floating plants, moss

• Gentle maintenance routine

  • Regular small water changes

  • Careful feeding (no overfeeding)

• Experienced keeper

  • The person can read the tank’s “mood”: smell, water clarity, plant health, animal behaviour

In this kind of system, it’s possible to:

• Use no filter, or

• Use only a very small filter for light water movement

The plants + substrate + bacteria become the main “filter”.

But this style is not very forgiving if:

• You suddenly overfeed

• You add too many fish at once

• You neglect maintenance

• You are still guessing about water quality

So I don’t see it as “better”. I see it as:

A special style that demands patience, observation, and discipline.

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4. When a Filter Is Your Best Friend

Now let’s be honest with ourselves as home hobbyists.

A filter becomes very helpful when:

• The tank is small (nano tanks crash faster)

• You have fish + shrimp, not only a few shrimp

• You like to feed a bit heavier

• You don’t have time to sit and observe the tank every day

• You’re still learning how to read water and plant signs

In these cases, a filter gives you:

• Extra safety margin

• More surface area for bacteria

• Better oxygenation

• More time before waste becomes a serious problem

For shrimp tanks, a gentle filter (often sponge or pre-filtered HOB) also:

• Keeps particles from building up too much

• Circulates food and oxygen

• Still allows shrimp to rest and graze calmly

So instead of thinking:

“Filter = not natural”

I prefer thinking:

“Filter = a helper that supports my natural system
so it doesn’t collapse the moment I make a small mistake.”

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5. “Natural” Does Not Always Mean “No Filter”

Sometimes we mix two different ideas:

• Natural look

• No equipment

A tank can be:

• Full of wood, leaves, plants, roots

• Gentle, brownish water

• Peaceful and slow

…and still use a small, quiet sponge filter hidden in one corner.

You still get:

• The comfortable, forest-stream feeling

• Natural behaviour from your animals

• Extra bacteria, flow, and oxygen from the filter

So we don’t have to go to extremes like:

• “If I use a filter, my tank is not natural.”

• “If I don’t use a filter, my tank is superior.”

We can simply ask:

“For my lifestyle, my water, my animals,
is it safer to have a helper (filter) or not?”

Most of the time, especially for beginners, the answer is:

Yes, a gentle filter is a good idea.

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6. Special Case: Shrimp Tanks

Since a lot of your readers will be shrimp lovers, let’s zoom in there.

Shrimp tanks have a few special needs:

• Shrimp are sensitive to ammonia and nitrite

• They like stable, oxygen-rich water

• Baby shrimp are tiny and can get sucked into strong intakes

That’s why many shrimp keepers like:

• Sponge filters

  • Gentle flow

  • Huge surface area for bacteria

  • Safe for shrimplets

  • Shrimp can graze directly on the sponge

• Or filters with pre-filter sponges on the intake

  • Protects babies

  • Turns the intake into a grazing surface

You can run shrimp tanks without a filter if:

• The tank is large enough

• Very heavily planted

• Lightly stocked

• Very stable and mature

• You are okay with moving more slowly and being extra careful

But if you:

• Want to sleep more peacefully

• Don’t want your shrimp to be on the edge all the time

• Are not 100% sure about your water yet

Then giving them a small, gentle filter is a kindness, not an enemy of “natural”.

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7. Thinking in Terms of Balance, Not Equipment

Whether you use a filter or not, your tank always obeys the same rules:

• Waste must be processed (ammonia → nitrite → nitrate)

• Oxygen must reach your animals and bacteria

• Plants and bacteria need time to adapt to changes

• Overfeeding and overcrowding will always cause trouble

So instead of asking:

“Filter or no filter?”

A better question is:

“How much biological support does this tank need
based on volume, animals, plants, and my habits?”

For example:

• 20L tank, 3 fish, some shrimp, moderate plants →
  A small sponge filter is a very smart choice.

• 80L tank, deep soil, jungle plants, only shrimp, experienced keeper →
  Filterless might be possible, or just a tiny air-powered sponge.

You get to decide how much safety net you want.

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8. How This Connects to Your Future Filter Choice

This post is more about philosophy and understanding:

• Filters are not the enemy of natural tanks

• Bacteria live everywhere, not just in filters

• Filterless tanks are possible, but not automatically “better”

• Beginners are usually safer with a gentle filter

Water Basics Series — Wander Within Life

1. Soft vs Hard Water
2. GH, KH & TDS — The Three Numbers
3. No RO, No Distilled: Can I Still Keep Shrimp?
4. Do We Really Need a Filter? (You’re here)
5. Filters for Shrimp Tanks — Flow • Intake • Media
6. How I Treat Tap Water Before It Enters My Aquarium
7. Pothos as a Natural Filter — Roots in Water, Leaves Above