There are many types of sand available, but keep the following things in mind when making your selection:
It must be safe for saltwater aquariums.
If you choose something that is too fine grained, you may have sand-storms later. Reef tanks require a good amount of water movement and this can cause the sand to shift.
Some creatures require finer grained sand and some fish sleep buried in the sand. Some types of anemones require a deep sand bend, so think about what you want to keep in your tank before you make a final decision on sand.
Black sand is an attractive alternative, but it has magnetic particles that will interfere with a magnetic algae scraper.
Live and Dry Sand
Just like rocks, sand is sold in a live" form that contains bacteria as well as dry, which does not. Unlike rocks, packaged live sand is unlikely to contain pests, so it is safer to use. I generally include at least one bag of live sand when I start a new tank.
Even if you visit your local fish store to look at their sand offerings, it is difficult to get a sense of the grain and the color, but it may be worth it.
CaribSea is one of the leading sellers of sand and has a very good web site that shows you the color and grain of their products. Their "Special Grade Reef Sand" is a good compromise between looks and a grain that is not too fine.
For this tank, I'll be using CaribSea Aragonite sand that I had leftover from my last tank. I have several 10 lb bags left, but I think 2 will do. I bought it at Petco for $4.95 per bag and it was shipped for free.
How Much Sand
A rough estimate is one pound per gallon of water in your tank but this varies greatly. It depends on how deep you want the sandbed to be. If you buy it at your local fish store, you can always return what you don't use - or keep it for your next tank!
Washing and Placement
Before we put the sand in the tank we need to wash it thoroughly. Dry sand is very dusty and will lead to cloudy water although that will clear up quickly.
Put some sand in a bucket, but don't fill it more than 1/4 full.
Use a garden hose to spray it while you stir the sand with your hand and let the dirty water overflow the bucket.
Do this until the water is as clear as you can get it and then take the bucket to the tank and dump the sand in, or use a large spoon to place it in between the rocks.
I went outside, put down a chair and brought the garden hose close to me. Then, I got two empty buckets: one to rinse the sand and another to hold the clean sand. Then, I brought over the two bags of sand and rinsed half a bag at a time. All in all, it took about 30 minutes. Then, I brought the bucket of clean sand and placed it on a chair close to the tank. I used a plastic spoon with holes to pick up the sand and drop it in the tank and my fingers to level it a bit. I ended up using less than the two bags.
Don't worry if you get some on the rocks or if it's not perfectly even, that's easy to fix later.
It's starting to look real! Now let's talk about water.