Using Sand for Aquarium SubstrateI absolutely love sand in my aquarium. I started off with gravel but within a couple of years migrated across to sand and now would never go back to gravel. Many fish actually prefer sand, some fish actually require it for natural spawning behavior. Many of the lakes in Africa are all sand so it would make sense to use sand if you're keeping these type of fish. I think fish find sand easier to move around and it may actually reduce the risk of injury to their mouths as well. Some fish such as Jurupari, also known as Eartheaters sift the substrate, probably looking for tasty morsels, you can actually see the sand falling back through their gills, I think they would have a pretty hard time doing the same with gravel. There are quite a few readily available sands that people use in their aquariums. The most common is probably play sand, this is often sold in most building and hardware stores, it's typically used for sandboxes and in the building trade. You also have Silica, also sold as blasting sand. There is also sand that is known as Black Beauty. This is actually iron slag and not sand, but people still use it quite often in their aquariums. Then you have Coral Sand, this is mainly sold in fish stores. Black Tahitian Moon Sand is also available fish stores.
Before putting sand into your aquarium it's recommended that you give it a good clean. You clean sand in very much the same way as you would gravel. Using a reasonably large bucket, pour some sand into the bucket, don't put too much in, probably a quater of a bucket full of sand would be okay. Then add water and start swilling the sand around. After two or three minutes carefully tip the water out of the bucket and if need be repeat the process until the water runs reasonably clean. You're never going to get the sand totally spotless, you just want to remove the worst of the dust.
I would recommend you have between 1 and 1½ inches of sand in your aquarium. If you are adding sand to your aquarium with no fish than just pour the sand in and level it off once you're done. If you are swapping from gravel to sand then it's just a case of removing the gravel before you add the sand. The fish will be okay as long as you take it easy, however if you want to remove them whilst you carry out the process of removing the gravel then this will obviously mean you can work a little faster and will not need to worry about knocking them around accidentally. If you have got a good biological filter then you shouldn't have any problems replacing the gravel with sand. However your gravel will actually hold some beneficial bacteria so if you haven't got a particularly large filtration system you may want to take some of your existing seeded gravel and put it in a media sack, or even some pantyhose and place it near the filter intake. It doesn't have to stay there very long, maybe a week or two, your biological filter should catch up perfectly okay.
Many people seem to have a problem when it comes to cleaning sand. What you got to remember if you don't clean sand in the same way you clean gravel. Because sand particles are that much lighter than gravel, shoving your gravel vac directly into sand will probably result in you sucking loads of it straight up the pipe. I have found there are two ways that you can successfully clean sand using a gravel vac without sucking it all out. One way is to hover just above the sand so you don't actually suck it all up. Because most of the crap and debris lies on top of the sand you can easily remove most of the debris without removing the sand as well. Another way I have found of cleaning sand without sucking it all out is to actually angle your gravel vac rather than pushing it perfectly into the substrate. It might take a little bit of practice before you get to it off to a fine art but once you master it you'll find cleaning sand is an absolute doddle and takes half the time it does cleaning gravel.