It is sand that (1) was taken from a coral reef, and (2) has many micro- and macro-organisms living in it. These organisms are present naturally. They help balance the reef tank by providing a natural food source for the inhabitants of the enclosed reef, and by providing and encouraging bacterial water purification (nitrification and denitrification).
Do I need all live sand?
No. You may use all live sand (and if money is no problem, that is fine), but live sand is expensive. It is not as costly as live rock, but it can still add up. I have used a half-and-half mixture: one-half actual live sand and the other half a material called “aragonite,” by CaribSea. This material is designed specifically for reef tanks and live sand filters. It has all the desirable qualities without the hefty price (aragonite costs about $1 a pound). When you use this 50/50 mixture, the live sand will colonize the aragonite material, so that eventually the mixture will become all live sand.
One factor to consider: the amount of die-off on live sand is unpredictable. If you use all live sand, it will take some time to cycle. It is a biologically dense material containing millions of bacteria and other organisms, and it is rich in both living and dead life forms. As stated in the section on power outages, oxygen is needed to keep most organisms alive. Shipping and handling of this sand material can take its toll on the organisms living in it.
Another thought: when purchasing the sand, you can’t really tell its quality by looking at it, as you can with live rock.
Can I use any sand for the job?
No. You should use only live sand or aragonite material. Regular beach sand, play sand, or home improvement type sand will most likely have silicate in it, which will be sure to cause problems with algae, which will be next to impossible to remove. Ordinary sand may also have “who knows what” in it, so don’t use it. Use only material recommended for reef tanks.
How much sand will I need? For a recommended thickness of approximately 1-3/4 to 2 inches, you will use 1.45 pounds of sand per gallon. For a 55-gallon tank, this is 80 pounds. It may interest you to know that this works out to the same per-gallon amount as is recommended for live rock. It seems that 1.45 or 1.5 pounds of live rock or sand per gallon is the maximum amount to put in the tank.
Simplified Reefkeeping
