Why use live sand?
Live sand is similar to live rock, in that it gets its name from the live bacteria and micro-organisms that live in it and on it, the sand itself is not alive. The benefits to using live sand in the saltwater aquarium are similar to the benefits of live rock. The sand provides additional biological filtration, while also providing specialized cover for fish such as the Wrasse and Goby varieties, which either hide in the sand when startled, or dig burrows and make themselves at home.
When keeping live sand in a saltwater aquarium, generally a sand bed depth of 2 to 3 inches is normal if you are planning to keep any of the tunneling gobies or wrasses. Live sand does have a bit of a special maintenance requirement to it that is very important. A deep live sand bed such as two or three inches will need to be stirred up and turned over and sifted regularly, but this can be done by hiring the right work crew for the job.
Maintaining live sand
The work crew will be various invertebrates, and sometimes a few fish as well. The hardest working sand stirrer you will want for your sand bed will usually be Cerith Snails. They are small and very active, but you will rarely ever see them because they spend most of their time buried in the sand. If you have a large tank of 100 gallons or more, you might consider adding a sand sifting starfish but only add one. They are so active and so efficient that they may starve if you add more than one, or do not have a large aquarium full of sand for them to sift through. Adding some small sand dwelling and perching type fish would also be a good way to help stir up the surface of the sand as well as beneath the surface. Not having the sand bed stirred properly and turned over fairly regularly can result in issues with trapped toxic gas pockets that can be harmful to the aquarium.
One common question asked by those who are new to keeping live sand is, “Do you vacuum the sand the way you would gravel?” The short answer for this is no, you do not. Some people have worked out a technique to skim the debris from the surface without removing very much sand, but the general rule of thumb is that the sand may be manually and lightly turned over from time to time but it does not get vacuumed.
Types of sand
Adding already established live sand into your aquarium is a great way to go, because it really kicks the tank into an established mode much more quickly. However, you can add standard non live saltwater sand to the aquarium, something along the lines of aragonite sand, and if given enough time it will eventually become live sand. The advantage of using at least part already established live sand in the aquarium is that the diversity of life in micro-organisms will tend to be much higher than what will form on its own in the aquarium without being seeded.