Why change from CC to SSB or DSB?
Most of us will not use crushed coral because it is a large substrate that traps the fish waste and uneaten food that has to be vacuumed before it creates nitrates, which it will anyway. Crushed coral does not provide a very good biological zone, and many tanks are setup with CC from the get go through lack of knowledge or because it is the only substrate that an LFS sells and tells you that it is all you need, using a selling point of CC has buffering power. I have personally battled nitrates over 100 ppm during my days of CC and UGF doing frequent large water changes. So many of us have been there and had high nitrates, did a water change to lower them and they were back in a couple of days. CC has sharp edges, which is undesirable for inverts, like anemones walking around, pods or worms. No getting around it CC is high maintenance and can lead to poor water quality, frequent maintenance, sick livestock, algae blooms and more.
Sand on the other hand has more benefits. These include having far more surface area thereby making it able to handle a higher bio load of bacteria. It is less dangerous to your infauna and has a more natural look in the tank. If going with a DSB Deep Sand Bed you can have other benefits as well like finishing the denitrification or providing sand sifting, burrowing, or tunneling fish and critters a place to play. The denitrification process predominantly occurs in deeper substrates and in areas of stagnant flow where oxygen levels are depressed. And this is why deep sand beds are effective as a nitrogen export mechanism. As water slowly diffuses deeper, aerobic organisms strip all available oxygen for respiration. In the deep, oxygen-deprived layers, denitrifying anaerobes are given the opportunity to convert nitrogen compounds into nitrogenous gases, which escape via tiny bubble out of the aquarium. I believe this process can also work on a limited basis in shallow sand beds. My sand bed is no more than 2 inches deep in some spots.
So what sand do I use to build my sand bed?
The answer here is aragonite sand. Many hobbyists have found that Southdown, Yard right or its apparent new name of old castle sand works very well for reef aquariums. This is due to it being calcium carbonate based, and with an excellent grain sizes makes for a good functioning sand bed. 1/8mm is very fine> 1/256mm to 1/16mm is considered silt, and less that> 1/256mm is considered clay.
Southdown seems to mostly contains very fine to silt size particles, and maybe a few larger than 1/8mm.
Other aragonite sands are available through many LFS. If it is aragonite it is good.
The trick here is to make sure that it is aragonite and not calcite sand as many different minerals have identical chemical formulas but wildly different properties. Aragonite is orthorhombic crystal and calcite is rhobehedral, scalenohedral or prismatic crystals
This means they have a different arrangement of atoms giving them different properties of density, solubility, hardness etc. They also tend to incorporate different trace elements, based on what best fits into their different crystal structures. Aragonite will substitute larger atoms such as strontium. Calcite grabs magnesium and iron. Aragonite’s properties are much more beneficial in a closed system.
It also seems that many have used Quick Crete play sand with success though it is not calcium carbonate based, but silica based instead. No this does not mean that you will have silicates in your tank.
Very Generally speaking Silica sand, lets say industrial style is a high purity quartz (SiO2) sand. Silica is a stable compound and will not leach silicates into your tank for it has no "sillicates in it. Depending on its chemical and physical characteristics, silica sand is used as glass sand, foundry sand, abrasives ..etc. Silica sand can contain tiny amounts of impurities, such as iron, manganese, chromium, calcium, or aluminum, and give the sand its color depending on how much of these impurities are contained within. So it depends on geographically where your silica sand comes from as to how much impurities it contains. If you are going to use silica sand look for white silica sand as it is much more aesthetically pleasing
