Boost Your Saltwater Tank’s Biofilter With a Sand Bed

Categories: Rock & Sand, Aquarium Gear For Beginners

Last updated: Apr 08, 2022

Outside of a specific type of tank called "bare-bottom", using sand for substrate in your saltwater aquarium is extremely beneficial because it creates stability with a robust biofilter. In addition to that, it will provide suitable habitat and a natural-looking aesthetic that cannot be achieved any other way.

Functions of a Sand Bed

The term "sand bed" simply refers to the entire layer of sand in the bottom of your tank as a whole.

Biofilter

The millions of tiny sand grains that make up aquarium sand bed are often made from aragonite-based materials but can also be crushed coral, seashells, and even volcanic rock. Some sand is naturally collected and will contain a variety of different minerals. No matter what kind of sand you choose, the tiny grains will provide an incredible amount of surface area where beneficial bacteria will colonize. The bacteria can then quickly break down and convert fish waste, leftover food, and other organic materials into unharmful byproducts that are removed via water changes and filtration.

The sheer amount of beneficial bacteria the sand bed can support creates a level of stability in your tank that is not easily accomplished otherwise.

Habitat

Sand in your aquarium provides valuable habitat for a wide range of creatures including Nassarius Snails, Sand Sifting Gobies, Wrasses, and Pistol Shrimp just to name a few. There are also a variety of microorganisms like copepods, sandworms, and a variety of other small invertebrates that dwell and reproduce among the sand grains. These small marine invertebrates are often a highly-valuable natural food source for fish and other animals. That means that sand will not only provide habitat but also supports the growth of valuable living food sources in your tank.

Aesthetics

What is an ocean without white sand beaches and crashing waves? The addition of sand to your marine aquarium will dramatically improve the appearance and create that natural ocean aesthetic most all of us desire.

Types of Sand Beds

There are only two types of sand beds that are differentiated by vertical depth.

Shallow Sand Bed - A layer of sand that measures no more than 2" deep. A shallow bed is the best choice for a modern saltwater aquarium because it is easy to keep clean and supports a robust biofilter.
Deep Sand Bed (DSB) - A layer of sand that measures 4 - 8" deep. A DSB can be an effective de-nitrifying filter because it promotes the growth of anaerobic bacteria deep in the sand where oxygen supply is limited. They can be difficult to keep clean and tend to look really nasty because of all the biological activity and waste that gets trapped among the grains of sand.

How To choose Aquarium Sand

There are really only a few things to consider when buying sand. The options are limited and as long as you follow these steps, you will wind up with a successful sand material that looks great and won't cause problems.

1. Choose a color you like

Your options are white, off-white, and black (often with white speckles). Most of us choose some version of white because that is what looks natural. Black sand can scratch your tank and tends to look dirty as waste collects on top of the sand.

2. Choose wet or dry sand

Dry sand is the most affordable option and it must be rinsed before use in your aquarium. Wet sand (sometimes called live sand) comes with water/moisture in the bag and contains beneficial bacteria to help jumpstart the cycle process in a new aquarium.

3. Choose a grain size

Sand grain size can vary from as small as 0.25 mm in diameter all the way up to 8mm in diameter.

Sugar-sized: The smallest grain sand that measures < 1 mm in diameter. It looks great but can be a real pain because it is easily blown around your tank by even the mildest of water flow. Not the best choice for most saltwater tanks.
Special-grade: Medium grain sand that measures 1-2mm in diameter. This sand looks pretty good and is the most popular choice. It won't get blown about your tank unless there is considerable water flow or direct current pointed at the sand.
Crushed -coral: Largest grain sand that measures 2 - 8mm in diameter. This is usually crushed up coral skeletons or seashells. Most would argue it isn't the best-looking sand option and the large particles can collect some serious waste if not siphoned and cleaned often.