Salwater aquarium sand is one of the popular substrates. In this hobby, aquarists have four options: Crushed Coral, Live Sand (Deep Sand Bed), Live Sand/Aragonite (Shallow Sand Bed) and Bare Bottom (No Sand Bed).
In the beginning of the hobby Crushed Coral was the standard saltwater aquarium substrate. Both Crushed Coral and Live Sand will act as buffer and will provide calcium for corals if dissolved. Crushed Coral is ideal for fish only systems to prevent large fish from moving the substrate and potentially causing a Live Rock slide. It can also be useful in high flow reef aquariums, where ordinary live sand and aragonite would create a sand storm. The major disadvantage of Crushed Coral is it must be siphoned clean of debris as often as every week to prevent detritus from building up.
Deep Sand Bed
The Deep Sand Bed is popular amongst hobbyists around the world. Using a fine Live Sand, substrate is built four to eight inches deep. The fine live sand is easily blown around by pumps and powerheads, so precaution should be taken to prevent aquarium sand storms. The theory behind the DSB is anaerobic bacteria grow in oxygen depleted zones and convert nitrate into nitrogen gas. If properly maintained with sand sifters, like nassarius snails and sea cucumbers, the deep sand bed can provide excellent filtration for many years. Some hobbyists believe the deep sand bed is like a vacuum bag and once it becomes full, it will release harmful toxins, crashing an aquarium unexpectedly. Another disadvantage is a four to eight inch sand bed can take up a lot of visual space in a display tank.
Shallow Aquarium Sand Bed
The Shallow Sand Bed is a happy medium between bare bottom and a Deep Sand Bed. The Shallow Sand may be built one to two inches deep from fine live sand or more course Aragonite. The Shallow Sand Bed provides little bacteria to reduce nitrates, but is still capable of converting ammonia and nitrite into nitrate with aerobic bacteria like crushed coral. Unlike Crushed Coral, a shallow sand bed does not need to be siphoned, but will blow around in high flow aquariums if powerheads are not strategically positioned. The Shallow Sand Bed requires the least maintenance of the four described methods.
No Aquarium Sand
The Bare Bottom aquarium uses no substrate and relies on heavy water movement to keep detritus from settling. Many reefers keeping SPS corals have fallen in love with their Bare Bottom systems. They are able to move high volumes of water without worrying about creating an aquarium sand storm. Most Bare Bottom systems are also designed to be low nutrient systems to enhance coral color. Maintenance on a Bare Bottom system includes daily siphoning of detritus in dead spots. Unlike the other methods described, Bare Bottom systems provide no natural buffer against changes in pH, like Crushed Coral, Live Sand and Aragonite.
In summary, you can be successful with any of the described method as long as you provide proper maintenance. Each system has its pros and cons, select one that will best meet your needs and level of involvement. When you are ready to buy aquarium sand, be sure to start your search online to find the best deals and varieties.