Deep or Shallow Sand Bed in a Saltwater Aquarium

deep or shallow sand bed in saltwater tank

There is a lot of debate on a deep sand bed vs shallow sand bed for your saltwater aquarium.

A deep sand bed in your saltwater aquarium benefits your saltwater aquarium in many ways. A deep sand bed is commonly defined as a bed of fine sand with a minimum depth of four to six inches which ensures that a portion of the sand at the bottom will not be exposed to significant circulation of water.

An established deep sand bed consists of sand populated with bacteria, algae and other marine organisms such as worms, crabs, snails and stars. The creatures burrow and overturn the top two to three inches of sand in search of food, which causes water to circulate deeper in the sand than it would if the creatures were not present.

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Deep sand beds may be made of a variety of materials, but typically fine or “superfine” sand is used, such as carib sea brand, with a grain size between 1 mm and 0.05 mm. A larger particle size increases circulation, which in turn requires greater depth to establish anaerobic areas (no oxygen.) Larger particles can also inhibit the burrowing of small animals, which would limit circulation into the bed. Additionally, larger particles (2 mm or larger) are prone to detritus accumulation (fish waste), which necessitates periodic siphon cleaning.

Get the finest sand possible when creating a deep sand bed for your saltwater aquarium.

A finer, smaller grain sand such as carib sea is recommended for saltwater aquariums. A finer sand will not trap fish waste and uneaten fish food, which will rot and cause issues in your saltwater tank.

A deep sand bed also benefits anaerobic bacteria, which feeds on nitrates in the very low oxygen areas of your aquarium. Anaerobic bacteria live in low oxygen to no oxygen areas of your saltwater tank (deep sand beds have little to no oxygen in the deeper levels of sand.) Anaerobic bacteria live in these low oxygen areas and break down the bad stuff in your saltwater aquarium.

deep or shallow sand bed in saltwater tank
Deep Sand Bed in saltwater tank

Never disturb the deep sand bed in your saltwater aquarium

When you vacuum your saltwater aquarium make sure to not let the vacuum penetrate the sand, as this will disturb the thousands of bacteria and creatures that are needed to keep your saltwater aquarium healthy.

Read on to discover what kind of sand is best for your salt water aquarium (also known as marine aquarium) and get the truth about how deep your sand bed should be.

A shallow sand bed (2″ or less depth) has advantages and disadvantages over deep sand beds. To help decide what you need, you need to decide what you want to achieve.

A shallow sand bed measuring 1.5? to 2? deep with a fine grade sand is great for a natural looking, brilliant sand bed. The CaribSea Fiji Pink and Aragamax are the two most popular fine grade sands. The fine particle size is great for filtration because there are tons of surface area for bacteria to grow on.

A shallow bed is easy to keep clean and will not clog up with detritus (fish waste.) Because the sand is fine and lightweight, it can get blown around easily in reef aquariums with high water flow and you can end up with bare spots on the bottom of the tank. This is easily-fixed by adjusting your power heads in your aquarium.

Using a deep sand bed with fine grain sand is great because of the increased biological filtration.

A deep sand bed will promote both aerobic and anaerobic bacteria, helping to break down waste and remove nitrates from your saltwater tank.

A deep sand bed is typically 6? to 8? deep. Within the first 2 to 3 inches, aerobic bacteria will thrive and help breakdown waste and produce nitrates.

As you go deeper into the sand bad, the water will be less oxygenated and therefore anaerobic bacteria will thrive. This type of bacteria is very efficient at denitrification which will turn nitrate into nitrogen gas.

The drawback to a DSB (deep sand bed) is that you need much more sand and it takes up a significant portion of your aquarium. Additionally, there is also the potential for pockets of poisonous hydrogen sulfide to develop if there are not enough organisms to keep the sand bed stirred and clean.

Allowing a deep sand bed to become stagnant and full of detritus (fish waste) will eventually cause a big problem in your tank so be sure to maintain a solid clean-up crew with animals such as nassarius snails, sand sifting gobies and starfish, sea cucumbers, conchs and even hermit crabs.

With coarser sand (larger sand grain), you will have less surface area for bacteria to grow on and a higher chance of detritus getting trapped in the sand. The advantages are that because it is heavier, larger grain sand does not get blown around your saltwater aquarium easily and you are less likely to have bare spots at the bottom of your aquarium.

Coarser grain sand can also be cleaned with a gravel vacuum during water changes so it is easy to keep clean and free of detritus.

A coarse grain sand bed that is more than 2? to 3? inches deep is a dangerous combination because it will quickly become clogged with detritus and increase the nitrate in your tank. 

Use a fine sand for deep sand bed setup in your saltwater aquarium. You will also have a much greater chance of getting toxic pockets of harmful gas and it is difficult to keep clean, even with a hefty clean-up crew if a larger grain sand is used.

Once you have decided on the type of sand bed you want, you will have some options when it comes the appearance and color of the sand. 

CaribSea Aragamax and Oolite sand have sort of become the standard for fine grade sand. Both are fine, beige-colored sands that are uniform in color and size.

The CaribSea Fiji Pink and Bimini are also beige colored, fine grade sand with small bits of pink mixed in which gives it a very unique and natural look.

I have 200 pounds of this CaribSea Fiji pink sand in my 125 gallon saltwater aquarium.

With so many choices and the dramatic way sand can transform the appearance of an aquarium, you now see how this is really a worthwhile topic to consider while planning your aquarium build.

Deep Sand Bed Pros– a great big sponge for absorbing phosphates and removing nitrates.

Deep Sand Bed Cons– Deep sand beds will need to be completely replaced at some point. Some reef keepers have kept deep sand beds for 8-10 years. NEVER stir or vacuum through a deep sand bed! This will kill microscopic life that keeps your saltwater tank healthy!

What are your thoughts on deep or shallow sand bed and which one do you have? Let us know in the comments below.

Thanks for reading!