Deep Sand Bed – No Water Change in Fish Tank

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Many things play an important role in an aquatic system’s stability and overall health. The most important one is, by far, the filtration system.

Whether it’s artificial or natural, the filtration system is a vital component, keeping the system stable and providing the aquarium with efficient chemical exchanges.

In short, the filtration system eliminates waste, debris, bacteria, and chemicals, keeping the environment cleaner, healthier, and more well-oxygenated.

That being said, artificial chemical systems require cleaning and maintenance. Wouldn’t be nice if we had a self-sustainable system that works unguided?

Fortunately, we do, and it’s called a deep sand bed (DSB). Having a deep sand bed in your aquarium eliminates the need for water changes, as the system will become self-sustainable. Or so they say. But let’s get into the deeper details.

How Deep Sand Bed Filtration Works?

The concept of deep sand bed is fairly easy to understand, but it takes more explaining to get a full picture.

DSB is practically a sand substrate, except it comes with 2 main differences compared to normal sandy substrates:

  • It’s deeper – Standard depth recommendations for sand substrates fall in the ballpark of 1-3 inches. The substrate‘s depth depends on the plants and fish you’re housing for the most part. DSB goes double that in-depth, reaching at least 5 inches. We’ll discuss why this value is so important.
  • It’s alive – DSB relies on live sand. Live sand is nothing more than bacteria-filled sand, functioning as a natural filtration system. Live sand is of two types: natural, coming straight from the ocean, around live coral systems, or human-made. The latter is obtained by growing cultures of live bacteria in the sand to replicate its natural counterpart.

So, it’s now all clear that live sand, the one used in DSB, is filled with countless bacterial cultures. But how do these affect water quality? I have 2 words for you: anaerobic bacteria.

These form the aquatic system’s lungs and kidneys by consuming environmental nitrates and keeping the water cleaner and safer. But we have 2 problems here:

  • The trade-off – While anaerobic bacteria consume nitrates, they produce hydrogen sulfide in return. This isn’t a great trade-off since hydrogen sulfide is toxic. This would be a reason for concern if hydrogen sulfide wouldn’t transform into sulfate in the presence of oxygen. Except it does, and there’s a lot of oxygen in the aquarium water to diffuse the dangerous hydrogen sulfide. However, this takes us to the second issue.
  • The notion of anaerobic – Anaerobic bacteria live in anoxic environments (completely deprived of oxygen.) This means you already have a problem since all of the anaerobic bacteria will dig themselves into the substrate, forming anaerobic pockets with deadly long-term consequences. Anaerobic pockets form under sand and consist of accumulated hydrogen sulfide and ammonia. Stirring the sand will cause these to pop, releasing the concentrated toxic chemicals into the water, often with lethal outcomes.

Given this issue, can you make deep sand beds work reliably and safely in your tank? Let’s get into that!

Can Deep Sand Bed Work in Freshwater Aquarium?

Yes, deep sand environments are sustainable in both saltwater and freshwater systems. It all boils down to the system’s setup and the steps you take to make it work.

 Anaerobic pockets are the biggest concern when discussing sandy substrates; work that, and there’s no reason for your freshwater aquarium DSB to fail.

Is Deep Sand Bed Good?

Yes, deep sand bed is a good natural filtration system, but I wouldn’t say it completely replaces the standard filtration units. DSB is good for moderating the amounts of nitrates in the water but cannot provide the entire spectrum of benefits of a high-end filtration unit.

Denitrifying bacteria is essential in any well-cycled environment, as they provide chemical balance and prevent the accumulation of dangerous chemicals like hydrogen sulfide, nitrates, and ammonia. The problem is that the concept of tank filtration goes beyond those several chemicals.

You also have mechanical filtration aimed to clear the water of larger particles, food residues, fish waste, and organic matter floating in the tank.

You also have biological filtration that eliminates various bacteria, viruses, fungi, and various other pathogens.

Finally, filters based on activated carbon tackle a multitude of dangerous chemicals that may seep into the tank water. These include ammonia, chlorine, chloramines, and other life-threatening chemical agents.

So, don’t expect your bio-filter to handle all these aspects since it can’t. That being said, DSB is quite effective when crafted and maintained properly.

How do You Maintain a Deep Sand Bed?

The long-term maintenance process is easier than it might sound. In essence, the main danger is the formation of large anaerobic pockets which can hold impressive quantities of hydrogen sulfide.

This gas will darken the sand in the pocket area and show as black when spilling into the water. We’re talking about extreme cases where the situation is already too advanced.

So, you only have one reliable solution to prevent the formation of anaerobic pockets, and it comes in the form of sand stirrers. These should be small and slow critters that would dig into the substrate, bursting any anaerobic pockets before growing too large.

They will pretty much aerate the sand and prevent the accumulation of dangerous hydrogen sulfide and other noxious gases.

Consider adding snails, sea stars, sea cucumbers, worms, and copepods, to name the most reliable ones. The latter are small crustaceans practically omnipresent in saltwater and freshwater environments.

So, they will adapt to any aquatic setup, provided their system is stable and healthy.

Stay away from animals like hermit crabs and conches. These animals are extremely voracious and will clean your tank of most other substrate dwellers, including those responsible for keeping your DSB stable.

Don’t stir the sand yourself since you will disturb the environment and cause potentially massive bursts of hydrogen sulfide to be released into the water column.

Rely on your substrate diggers to release it slowly and gradually.

How Much Sand You Need for Deep Sand Bed?

The official recommendation is around 5 inches, but this isn’t always the case. Depending on your tank’s size and overall system layout, you may need to go for 3-8 inches. The types of plants you’re using and your aquatic life.

If the sand substrate is too shallow, it won’t qualify as a DSB. If it’s too deep, the maintenance process will become more troublesome since the sand stirrers will take more time to cover the entire substrate.

To understand why your substrate needs to be deep, consider how DSB works:

  • The first 2-3 inches – This area is inhabited by aerobic bacteria. These can breathe oxygen and will thrive in this region since they’re getting plenty of it at this depth. These organisms are responsible for consuming waste and nitrites and turning them into nitrates.
  • The last 3-5 inches – At this point, the oxygen levels drop dramatically due to the sand’s compactness. Aerobic bacteria make room to anaerobic bacteria, which consume nitrates to produce nitrogen gas.

So, a thick-enough substrate is necessary to preserve the system’s stability and allow the formation of a self-sustainable micro-ecosystem.

What Sand is Best for Deep Sand Substrate?

If you’d ask me, I would recommend the most expensive type of live sand available. The idea is for the sand you’re getting to be life-rich and fine-grained.

The sand should be fine enough to allow the army of sand-digging critters to get in to perform their daily tasks.

Do You Need Other Filter in a Deep Sand Bed Tank?

Yes, you do. Some people rely on their DSB to ensure their tank’s filtration system, but I disagree. A lot of things can go wrong with DSB, especially in the hands of less experienced aquarists.

In essence, the deeper the DSB is, the higher the risks of hydrogen sulfide bubbles, releasing more chemicals than the system can handle.

This is where a proper filtration unit will come to the rescue. Many aquarists use activated carbon filters to dilute the hydrogen sulfide in case it reaches the water in larger quantities.

Such a filter is also useful for removing a variety of other chemicals that regular filtration systems cannot handle.

A mechanical filter may also be necessary, especially with all the substrate diggers roaming around. The filter will remove floating sand particles and eliminate food residues, fish poop, and dead organic matter accumulating on the substrate.

So, yes, I believe you need additional filtration power to keep your aquatic system between optimal parameters.


Deep sand bed can provide extensive benefits to any properly set-up aquatic system. You just have to be wary of the maintenance work necessary to keep the system stable long-term.

Do your research, get the best sand for your tank, and follow a reliable installation and maintenance guide for the best results.

Author Image Fabian
I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.
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