Sand is an excellent substrate for both freshwater and saltwater aquariums, but the price of sand at the local pet store can be quite high. One economical alternative to that overpriced pet store sand is the same play sand your children use in their sandbox. This play sand is sterilised to protect kids from harmful bacteria, and that sterilisation process makes the sand a good choice for aquariums as well.
Calculate how much sand you will need for your tank. To find the right amount of play sand, multiply the length of your tank by its width, then multiply that number by the depth of the sand. Divide the result by 20 to get the number of pounds of sand needed. For instance, if your tank is 24 inches long by 12 inches wide and you want to add three inches of sand, you would multiply 24 x 12 x 3 for a result of 864. Then divide that 864 by 20 for a result of 43.2. So you would need just over 19.5 Kilogram of sand to fill the aquarium to a depth of three inches.
Place your under-gravel filter in place if you will be using one. It is important that the filter reach to the edges of the aquarium to provide proper filtration.
Pour the sand slowly into the aquarium. Rake the sand smooth and even as you go. Continue to pour the sand in until you have the depth you want.
Anchor your plants, driftwood and tank decorations in place. Be sure to bury those items at least an inch down into the sand. Play sand is very soft, and it might not be able to hold the decorations in place as well as coarser sand. Making the sand a bit deeper around your plants and decorations is the best way to keep them in place.