No Water Change Tank?! Top Offs vs Water Change.

No Water Change Tank

Not long ago I received another letter (the third one!) about top offs and water changes. People asked me why do they still need to do water changes if they regularly do top offs? Well, every time I sent them almost the same classic answer.

In general, top-offs cannot replace water changes. It really does not matter how many gallons (liters) you add. The goal of water changes is to remove nutrients that build up over time in the tank. While the goal of top-offs is to replenish the water volume in the tank. Therefore, water changes should not be even compared to or related to top-off.

I am pretty sure that most of you do not even think another way. We have been taught these basic rules right in the beginning of the hobby. Right?

Well,… so much that we read about aquariums is just nonsense. What if I tell you that there is a way not to do water changes? Ladies and gentlemen’s fasten your seatbelt, I’m going to blow your mind.

Are Water Changes Necessary?

I would like to start off by warning you. Believe me, if you say on forums that water changes are not necessary, you risk starting such a sh@tstorm that it will cover you from head to toe!

However, there are examples where people manage to keep their tanks without water changes for years! YEARS! This is simply incredible. How is it possible? Is it possible at all or some kind of ‘dark magic’?

Actually, there is no deep secret behind it, just chemistry.

As I have said earlier, the goal of water changes is to remove nutrients that build up over time in the tank. Therefore, if we manage to remove the negative effect of accumulation of all bad things or processes in our tanks, we can skip doing water changes.

But how can we do it?

Conventional Understanding of Nitrogen Cycle

NitrogenCycle_DiagramFirst of all, the Nitrogen Cycle refers to the continual conversion of nitrogenous compounds. In simple terms, this cycle starts with fish, shrimp, snail, etc. waste material, which produces ammonia.

Ammonia (NH3) is toxic and, in the small confines of a tank, can eventually kill everything in the tank. Well, imagine you living in a small, dirty bathroom with a broken toilet.

Chronic ammonia toxicity can affect the reproduction, growth and immune system of your aquarium habitats. In some cases, it can even cause deformities.

However, it usually does not happen in a balanced eco-system. Why? Because in our aquariums we also have bacteria (Nitrosomonas sp.) which help degrade the ammonia to nitrites (NO2).

Ammonia nitrite nitrate formula

Nonetheless, this end product – Nitrites – is also toxic, so, another bacteria (Nitrospira sp.) will further downgrade the nitrite to nitrates (NO3) which is removed by the routine changing of the water.

Note: Getting rid of ammonia and turning it into nitrate is also called a nitrification process. During this process, to consume ammonia and nitrite, bacteria need to have the help of oxygen.

Here comes the most important part: Although bacteria in our tanks use oxygen to breathe as we do, some species of bacteria are more versatile and can live without oxygen available. How? Because they can start breathing nitrates! Not eating but breathing, because they still need carbons to eat.

Non-water Change Tank Setup

The reason why we do water changes is that we usually do not have the equilibrium, which exists naturally in the ponds or lakes.

When I am talking about equilibrium I mean – the true Balance of the input (mostly food) with the output (dirty water). It means usually that there is more food waste than the plants can consume. However, it is not just about plants, it is also about bacteria breathing nitrates.

So, what kind of tank do we need for a no water change setup? Can we do it in any tank? The short answer is – No. No water change tank setups have some specific requirements:

  1. At least a 10-gallon (40-liter) tank.
  2. Deep substrate (at least 10 cm or 4 inches).
  3. Fast-growing plants.
  4. A lot of light.

At first glance, there is nothing extraordinary. Lots of aquarists have close or the same setups. What is the difference then?

  1. Optimal feeding.
  2. Proper plant control.
  3. Understanding the processes in the tank.

Let’s take a look at each of these steps in a bit more depth.

Tank Size

A larger water volume is more likely to maintain stable water parameters. It can simply ‘absorb’ more contaminants without drastic effect on the fish, shrimp, etc. in the tank.

In addition, besides the fact that fluctuations are far more likely in nano tanks, large tanks allow using more substrate and plants, which is crucial for these types of setups.

Deep Substrate

Substrate plays one of the most important parts in no water change tank setups.

Do you remember that beneficial bacteria, which consume ammonia, then nitrite, turning into nitrates, need oxygen? What happens if there is no oxygen present?

Can bacteria still consume ammonia, then nitrite, turning into nitrates without oxygen? Well, they can! However, this time, instead of beneficial bacteria (which need oxygen), Heterotrophic bacteria (which does NOT need oxygen) will help us.

Some species of Heterotrophic bacteria can synthesize their own food by using organic materials. Instead of oxygen, they can also use nitrate in this equation. Of course, nitrate is not that effective as oxygen but it is the second-best thing they can use. These bacteria will convert nitrate into nitrogen gas, which will be gone from the tank.

This process is called denitrification.

Deep Substrate and Anoxic zones in tanksHow do we get Heterotrophic bacteria? Where is it?
Obviously, Heterotrophic bacteria will naturally occur in the lower level of the substrate where there is no oxygen present.

Depending on the type of the substrate, denitrification starts approximately at 5 – 10 cm (2 – 4 inches) down. It will be deeper in coarse substrates (for example, gravel) and more shallow in finer substrates (like sand).

As the water is slowly dissolving through the substrate at the top, the oxygen is going to gradually be used up and at the bottom, there will be a no-oxygen (anoxic) zone.

According to the study, for optimum results, dissolved oxygen levels should be less than 0.1 mg/l.

What about Anaerobic zones?

Now, you might think, wait a minute, did you forget about anaerobic zones? The thicker your substrate is the more anaerobic areas you are going to have. As a result, you will have Hydrogen sulfide pockets (H2S, it smells like rotten eggs) in the tank, which can kill your fish or shrimp.

Well, this is true … to some degree. Anaerobic bacteria producing Hydrogen sulfide usually take place in substrates deeper than 7 – 10 cm (3 – 4 inches).

The good news is that we can effectively neutralize the hydrogen sulfide in the tanks with oxygen.  Once hydrogen sulfide gas connects with oxygen it will return to sulfate form, which is not toxic.

Therefore, as long as your tank has enough oxygen, hydrogen sulfide should not cause any problem. So, we need to have a lot of oxygen in no water change tank setup. Add an airstone to aerate the water properly.

Note: This is another reason why large tanks are safer. Their water volume is big enough to safely dissipate the gas. In addition, the roots of plants will help to break up anaerobic pockets in the substrate (see below). 

A little bit of summary, now we know that we can have several types of bacteria in the tanks:

1.    Beneficial bacteria (Breath oxygen and degrade the Ammonia to Nitrites and Nitrites to Nitrates).
2.    Heterotrophic bacteria (Breath nitrates and turn it into nitrogen gas).
3.    Sulfate-reducing bacteria (Breathe sulfates and turn it into hydrogen sulfide).

Fast-growing Plants

We all know that plants are not just decorative. They can play a fundamental role in reducing aquarium maintenance. Which in turn affects the health of our fish, shrimp, snails, etc. For example, plants in the tank:

  • Oxygenate water,
  • Remove CO2,
  • Provide hiding, feeding, and breeding ground for the fish and shrimp,
  • Prevent toxic gas pockets in the substrate,
  • Provide more area for beneficial bacteria,
  • Help against the algae,
  • Provide additional filtration (let’s talk more about it).

When I am talking about filtration, I am not just talking about the nitrogen cycle. Of course, plants consume ammonia, etc. However, they also remove other chemical elements (metals) that are in the food that we put into the tanks.

This is a very important moment. Basically, the concept of no water change tank setup presumes the balance of:

  • What goes in – Food.
  • What goes out – Nitrogen gas (because of denitrification).

Obviously, food cannot be 100% transformed throughout the nitrification and denitrification processes into gas.

There will be still different minerals and metals in the food left. These ‘mineral leftovers’ will build up with time. Nobody knows when (it can be a year or two, maybe more) but eventually there will so many ‘mineral leftovers’ that they will change the balance and crash the tank. This is a fact.

To prevent this situation we need plants in the tank.

They can get rid of these ‘mineral leftovers’ and this is exactly why plants are so important in no water change tank system. They will not allow accumulating anything in the tank. Because this is not waste for them, these are nutrients they take up to grow!

As a matter of fact, one of the aquarists, Jay, conducted an experiment that lasted 10 months. Conditions:

  • No water change,
  • No filter,
  • Airstone only,
  • A very deep substrate,
  • No plants.

This is exactly what he is talking about. Check out his videos, they are awesome!

Plants and Nitrates

Plants, Nitrates, ammonia and ammoniumMost people falsely think that plants use nitrates to produce their proteins and grow. Strictly speaking, this is wrong.

Plants use ammonium to live and grow. For that, they need to convert nitrates back into ammonium. Unfortunately, it takes them a lot of energy to do so. In addition, they have to compete with beneficial bacteria for the ammonium.

Why is it important to mention?

Because nitrogen cycle is extremely complex. Ammonium, nitrites, and nitrates are always present in the tank. They can be undetectable by test kits, but they are always there.

Because plants will always ignore nitrates and take ammonium, it decreases their effectiveness in removing nitrates. This is the reason why we need a deep substrate with bacteria that can use only nitrates.

Lighting and Plant Control

Light is absolutely crucial for the photosynthesis required for the health and growth of all aquarium plants. They need this energy to absorb ‘mineral leftovers’, nitrates and grow.

Plant growth and development is another primal focus here. Because if plants do not grow fast enough, they do not eliminate ‘mineral leftovers’ and nitrites in the tank to create the balance.

To achieve this result, there should be a lot of plants … BUT the tank should not be overcrowded as well! The point is that if it has too many plants in there will be too much competition for nutrients. As a result, plants will not grow as fast as they can.

That is why trimming and taking out plants is the key part here.

Basically, we replace water changing (to remove nutrients that build up over time in the tank) with removing/trimming the plants (to maintain fast growth, so they can remove nutrients that build up over time in the tank). 

Read more about it in my article “Advanced Guide to Planted Tank Lighting”.

What Plants Can We Use in No Water Change Tank Setup?

There can be two types of plants:

  1. Main ones (they do the most job).

For example, Hornwort, Duckweed, Water Sprite, Water Wisteria, Frogbit, etc.

  • They grow fast.
  • Very hardy.
  • They are mostly floaters. Therefore, absorb nutrients from the water column.
  1. Secondary ones (they play a support role to maintain the system stable and safe).

For example, Anubias, Monte Carlo, Mosses, etc.

  • They do not need a lot of light and can live in shade (the main ones will absorb most of the light).
  • Relatively slow-growing, so they will not compete fiercely with the main ones for nutrients.
  • Provide additional filtration.
  • Most of them can be rooted. It will also help against hydrogen sulfide pockets in the substrate.

Bonus plants, Jack of all trades, Pothos plants.

Related articles:

  1. Top 7 Floating Plants for Beginners
  2. Submerged Aquarium Plants as Nitrate Suppressors
  3. How to Use Pothos Plants in a Shrimp Tank

Rules for plants, summary:

  1. Strong light (about 40 – 60 PAR).
  2. Tall tanks require more light.
  3. Use a light-timer on at least 10 hours per day.
  4. Only fast-growing plants to do the cleaning job.
  5. Not too many or too few plants. The density should be optimal to grow fast and absorb nutrients from the water.
  6. Constant trimming/removing to maintain fast plant growth.

Read more about it in my article “Advanced Guide to Planted Tank Lighting”.

Optimal Feeding

If you think that the main reason of ammonia in the tank is fish, snail, or shrimp waste you are only half-right.

Everything starts with the food we add there. I will repeat it again that the whole concept of no water change tank setups is all about the balance of Input (Food) with Output (Nitrogen gas). Obviously, the less food is going in, the less you have to worry about it.

This is the reason why shrimp tanks do not require frequent water changes compared to fish tanks.

Because we do not give a lot of food to our shrimp and they do not produce a lot of bio-load (waste). Therefore, it is easier to nitrificate and denitrificate it. Feeding less makes it way easier to accomplish a no water change tank.

No Water Change Tank Nitrification and DeNitrification

Understanding the Processes in the Tank.

Thus the overall process is accomplished by two different types of bacteria:

  1. Nitrosomonas bacteia– they perform the first step (nitrification) by converting ammonium to nitrite under aerobic (with oxygen) conditions.
  2. Heterotrophic bacteria – they perform the second step (denitrification) by converting nitrates to nitrogen gas under no-oxygen (anoxic) conditions.
  3. However, these bacteria cannot convert everything. Therefore, we need plants as the second line of defense. Plants absorb a ton of things from aquariums that we do not even think of. They are one of the essential filters for the aquarium. Their unique form of chemical filtration allows achieving the true Balance in no water change tank setup.
  4. Nonetheless, plants need optimal conditions where they can reach their full growing potential. The growth of plants ensures that they remove all mineral leftovers from the water.
  5. To be safe, install a basic filter in the tank. Although, some aquarists completely rely on plants and bacteria as a natural filtration. For example, here:

In Conclusion

There is no set formula for true Balance. That is why establishing the equilibrium is quite hard in aquariums, because every setup is unique. Every tank setup requires different variables to control in the equation.

However, it is real. It is not a myth. With the proper attitude, it is possible to create a no water change tank setup where the only thing that you will have to do is top offs. The problem is that high-tech tanks usually require a tremendous commitment in time and money.

Related articles:


1.   Ecology of the Planted Aquarium: A Practical Manual and Scientific Treatise for the Home Aquarist. Diana Walstad. 1999.

2.    Identification of Bacteria Responsible for Ammonia Oxidation in Freshwater Aquaria. Paul C. Burrell, Carol M. Phalen, and Timothy A. Hovanec. 2001, pp. 5791-5800.

3.    Nitrospira- Like Bacteria Associated with Nitrite Oxidation in Freshwater Aquaria. Hovanec, T. A., L. T. Taylor, A. Blakis and E. F. DeLong, Applied and Environmental Microbiology, Vol. 64, No. 1, pp. 258-264.

12 thoughts on “No Water Change Tank?! Top Offs vs Water Change.

  1. Wow, you have explained, easily in detail the balance of nature. I was perplexed as how my tank could be so in balance. Was not worried about it, just curious as how it could be so little trouble. It tells me that indead people could live on Mars, excellently presented. Trouble is in this world most want perfection, crystal clear water, well thats about it, appearance. Appearance is rarely sustainable to be in balance with natural environments. My tank is choke a block with tannins, plants and fish, does not look good however, everything is breeding. Thanks for such a thoughtful artical, appreciate it.

    1. Hi Aaron,
      I tried my best and I am really glad that you liked it 🙂
      Best regards,

  2. Best manual ever.
    Its really great to know that the dream is possible
    Thank you

    1. Hi Moasam,
      Thank you for the kind words!
      Best regards,

  3. Wow, this is so cool!
    These “self-sustaining” aquarium setups have been a fantasy of mine for a long time now. They really do sound too good to be true! Yet, this website was very realistic about the process.
    I have a bit of a question, though.
    Could a shrimp-only tank rely solely on Java moss and Java fern?
    (Well, not devoid of snails, but aside from that, shrimp-only.)
    Could an equilibrium be accomplished by slow-growing plants if the bio-load is extremely low?
    I do believe that shrimp and snails have a lower bio-load than fish because they consume a lot of ammonia-producing filth in the water, like detritus and even dead shrimp.
    Also, what would be the most ideal bio-load capacity for a 10-gallon tank concerning cherry shrimp and trumpet snails? Maybe just 3 or 4 shrimp and 1 or 2 snails? I heard that cherry shrimp need to be kept in large schools to be content.

    1. Hi Wayfarin,
      Thank you!
      >Could a shrimp-only tank rely solely on Java moss and Java fern?
      Do you mean a no water change tank? If so, it will be extremely difficult to controle nitrates and mineral leftovers with relatively slow-growing plants. Therefore, I would no do that.
      >I do believe that shrimp and snails have a lower bio-load
      Shrimp do not produce a lot of waste unlike snails. Snails are waste factories. If you need low bioload – do not keep snails.
      >I heard that cherry shrimp need to be kept in large schools to be content.
      100% correct.
      Best regards,

  4. Thank you for that thorough article, it really helped me. One clarifying question though (I am a novice). Can I assume my tank is balanced if the water is clear and has, lovely sparse algae blooms and stays clear (for months now) ? Note that I have 3 1/2 gallon fresh water tank with 1 beta, 3 snails and I never change water

    1. Hi Donna,
      I need to know more about your setup.
      But if your water parameters remain the same (no ammonia, nitrites or nitrates), you have a fairly good ecosystem.
      Best regards,

  5. Was wndring about this as my nerites hibernated and had to get some floaters to get rid of the prblm,2 days after adding my water lettuce red root floaters and floating water moss they came out of hibernation and have been active since even though Iv done no water change for 3 wks now,nrmly 20%water change pw,,thinking of adding some freshwater clam to,,I’m using the nerite snails as a gauge as they will hibernate befor toxicity gets to high for my fish,,starting to wonder how much longer this can carry on which is why I looked at ur article

    1. Hi Alan Jones,

      I understand your situation to some extent, but the question isn’t entirely clear, to be honest.
      What are your ammonia and nitrate levels? Apparently, they are high enough for even snails to notice. Fast-growing, particularly floating plants, are an excellent way to reduce nitrogen levels in the aquarium.

      Best regards,

  6. Fascinating, but so complicated! I’ve had an aquarium running for 20 or 30 years (a couple of tank ‘moves’ in that time). Tropical freshwater community. I picked up the habit from my dad. I have NEVER done a ‘water change’. Plenty of plants, an occasional trim of those plants, a strong biofilter, moderate fish stock… and an occasional top up for evaporation. But no intrusive disruptive water changes. The idea seems ridiculous to me.

    1. Hi Paddy Eason,
      Congratulations to you, you were simply able to do this on an intuitive level 🙂
      Many people can only envy you!
      Best regards,

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