For Beginners: Substrate and Sand Beds

Substrate and Sand Beds

A lot of beginners look into sand beds because it seems more natural. However, most coral reefs have very little sand at the bottom. With a bare bottom tank becoming more common in the hobby, we will discuss the pros and cons of sand beds and how to install one properly.

The Pros and Cons Of A Sand Bed

There are many pros and cons to having a sand bed. However, successful reef tanks can be kept and maintained both with and without a sandbed. There is no clear right or wrong answer as to whether having a sand bed is better or worse for the overall health of the tank. However, having a clear plan up-front is helpful because adding or removing a sand bed to an already established tank can be tricky.

Pros of a Sand Bed:

  • Improves Tank Filtration: Like live rock, it acts as another home for the beneficial bacteria that process and remove tank waste. 
  • A Home for Organism and Certain Fish: Provides a home for clean-up crew such as cucumbers, nauseous snails, sand stars, and other beneficial organisms. It is also a source of food for certain types of fish, like gobies, and is a place to sleep for certain species of wrasses.
  • More Self-Sufficient Ecosystem: Provides nutrients and even food to corals and fish, making the tank ecosystem a little more self-sufficient.
  • Stabilizes Live Rock Formation: Acts as a cushion for live rock and helps keep the rock in place. Also, in the event of a rock slide provides something in between the rock and glass.

Cons of a Sand Bed:

  • More Maintenance: Requires extra time to keep the sand bed healthy.
  • Reduced Water Flow: So the sand bed is not disturbed, the amount of water flow is limited.
  • Traps Harmful Gases: Can trap nitrate and other harmful gases.
  • Cost: Live or dry sand is an additional expense for any tank.

Types of Reef Substrate

Below is a breakdown of the most common substrates available and the pros and cons of each.


The most popular sand type, aragonite, is made of calcium carbonate, just like coral skeletons. It is available in multiple grain sizes, ranging from coarse to fine sand.

  • Pros: The fine grain size is ideal for reef tanks with burrowing creatures or fish like gobies that prefer to pick detritus from the tank bottom. Naturally releases calcium carbonate into the water, which helps maintain a steady pH and provides another source of calcium for corals.
  • Cons: Be wary of high-flow spots. Finding a balance between a sand storm and enough flow to move detritus and keep corals happy can be a struggle. Always check the chemical composition as some types of aragonite, like oolite, can contain phosphate and other unwanted chemicals.

Crushed Coral

Crushed coral is crushed coral skeletons and usually provides a heavier and larger grained substrate.

  • Pros: The larger grain size allows for a higher flow which helps keep detritus from building up in the sand bed. 
  • Cons: The larger grain sizes provide larger spaces between each grain so that the media offers less protection and habitat for burrowing creatures. Also, the large spore spaces can allow detritus to build up in areas where the water flow is not strong.

How Much Sand to Add to a Reef Tank

For a decorative sand bed, we recommend a 1-½” to 2” sand bed. For a deep sand bed, we recommend a 6” to 8” sand bed. Avoid sand beds between 2” and 6” as they are generally unhealthy for a reef aquarium.

Deep Sand Bed

In a deep sand bed, the top 2”-3” in a deep sand bed is exposed to water circulation and oxygen, allowing beneficial nitrifying bacteria to thrive, which helps break down waste. Since water and oxygen do not penetrate the deeper parts of a deep sand bed, this allows anaerobic bacteria to thrive. These anaerobic bacteria, in turn, help remove nitrate from the water. When cleaning the sand in a deep sand bed, vacuum only the top 2-3” of the sand as disturbing the lower parts of the sand bed can cause the tank to crash.

Should I Run a Deep Sand Bed?

A deep sand bed can improve tank filtration as it helps remove waste and nitrate. It also acts as a home for burrowing fish and all sorts of other critters. On the flip side, a deep sand bed requires a lot more sand and takes up a significant amount of the tank volume. There is also a potential for toxic chemicals such as hydrogen sulfide leaching out of the anaerobic section of the sand if there are not enough critters to keep the sand stirred and cleaned. The sand also gets dirty, which for some folks is not a good look.

How to Add Sand to a Reef Tank

For dry sand, start by rinsing the heck out of the new sand in a bucket allowing water to overflow the edge of the bucket to wash away any impurities and silt. Do not rinse live sand as that will wash away all the good live bacteria in the sand. For an existing tank, add a little bit at a time. Adding a lot of new sand to an established tank may cause it a mini cycle. If that happens, do a water change and test the water daily until levels stabilize.

Maintaining the Substrate / Sand Bed

For a shallow sand bed, thoroughly clean it at least once per month with a siphon. On the other hand, deep sand beds require less maintenance as intensive cleaning can be harmful.

There is no right or wrong answer on whether or not a sand bed is good or bad. For most folks, the ultimate decision to have a sand bed or not comes down to a personal choice of whether they like the look of a tank with or without sand on the bottom.

Have a question? Need supplies for your aquarium? Give us a shout here or visit our store locator to check our products today. Happy Reefing!

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