Choosing the right sand
The choice of sand is very important. Some sand will have no effect on water chemistry while some will buffer the GH/KH and/or pH. In addition, the cost and availability of the sand may also have an influence on your choice.
We can divide sand materials commonly used in two category: silica based sand and calcium based sand. The first category of sand should have no influence on the water chemistry while the other will buffer the pH and/or GH/KH. An African cichlid tank will probably benefit from calcium based sand while American cichlid tank will do much better with a sand what won’t change the water chemistry.
If unsure, the best thing to do is to test the sand before to use it. To do so, simply put some sand in a jar with water and test the water after a few days.
Silica-based sand
The types of silica sand typically used in aquarium are play sand, pool filter sand (sold for use in swimming pool filters), sandblasting sand, and some other sand labeled for use in freshwater aquariums. The grain size and shape may vary from one to an other but at the end, they are all silica sand.
Play sand
CEC : Low
Inert : Should be (assuming it is pure quartz). May contain calcium carbonate which may raise your pH undesirably.
Organic : No
Advantages:Look very natural and is cheap. The particles in play sand are usually too small and have very sharp edges.
Inconvenient: The particles are really small and can get sucked into the filtration system and completely destroy pumps in hours. So make sure to keep your pumps away from the substrate.
Pool Filtration Sand
CEC : Low
Inert : Yes
Organic : No
Advantages:The grain is smooth and round: no sharp edges. Even if it gets into your filtration system, it is not nearly as destructive as other type of sand. The best part of pool filter sand is the appearance; it looks very natural and the fish seem to love it. It is heavier than play sand. Pool filter sand is generally clean so less need to wash it before to add it to the tank.
Inconvenients: May be expensive.
Sandblasting sand
CEC : Low
Inert : Yes. Assuming the silica sand you obtain is pure quartz, it is no more soluble than the glass (also a silicate) that makes up your fish tank.
Organic : No
Advantages: Can be purchased in different grades that would allow for a large enough grain to ensure it would not be sucked into a filter.
Inconvenient: The main problem with sandblasting sand is cost (50 pounds can be around $100)
Calcium-based sand
Unless I am wrong, most calcium-based sand on the market are actually made of crushed coral, also known as aragonite. They are usually available in various grain size, from very small to very big. Aragonite sand is commonly used to buffer the water in African cichlid tanks and saltwater aquarium.
Coral or Aragonite sand
CEC : Low
Inert : Should be. May contain calcium carbonate which may raise your pH undesirably.
Organic : No. Will buffer your pH.
Advantages: A good choice if you need to stabilize your PH or improve your buffering capacity.
Inconvenient: It is fairly expensive.
Washing the sand
Whatever the sand you chose it is very important to wash it before to use it. Some sand such as pool filtration sand might not need to be washed as much as play sand but still, it is always a good idea to give it a good wash. If you don’t, chances are to cloud the water. Washing the sand is easy. Simply put the sand in a pillow case or a large paint strainer (my personal favorite) and run the hose in it.
Conclusion
Once we’ve decided if the substrate should buffer the water or not, there is no much choice left. At this point, price, the grain size and the colour are the main feature to look at.
