What do I have to consider when using sand as bottom material?
What do I have to consider if I wish to set up an aquarium with sand (fish, plants, cleaning, which sand, how much, advantages and disadvantages)?
Sand is generally well suited for aquariums, there are just two things to consider: The sand must be round grained (see "Types" below for details), and its grain size should be rather uniform, as to prevent small particles sinking into the gaps between larger grains where they would inhibit water circulation.
Some details about the mentioned items:
Fish: No fish has any disadvantages, but many will benefit from advantages (all species that search for food at/in the bottom or temporarily burrow into it).
Plants: There are no disadvantages, provided you make sure the water circulation within the bottom ground is not inhibited too strongly by uneven grain sizes. The main advantage is that the plants can very easily grow their roots in sand. Also in nature, plant growth takes place particularly well in fine grained bottom ground.
Cleaning: Cleaning the bottom ground is usually hardly ever necessary, as waste products (fish waste, uneaten food etc.) do not even sink into the sand. Trumpet snails are helpful and useful as they loosen the bottom ground (they are therefore sometimes nicknamed 'aquarium earthworms').
If you really need to clean the sand once in a while, it is sufficient to siphon it with a gravel washer - but with low suction as to prevent siphoning the sand out of the tank as well!
Types: It is important that the sand does not contain nor release any toxic substances (e.g. heavy metals) and, as mentioned previously, that it is round grained. Never use crushed sand, this might cause very unpleasant fish injuries! If in doubt, rub a sample of the sand between your fingers - you will feel whether it is round grained or sharp edged!
From a chemical/mineralogical viewpoind, the common sand consists of quartz. Quartz sand is bright (almost white to ochre).
Dark types are less common and more difficult to get. Garnet sand (reddish) and basalt sand (almost black) are well suited for aquariums.
Amount: A layer about 5 - 7 cm thick will be used in most cases. You can calculate the amount (in kilograms) by first calculating the volume in liters. This is done by multiplying length, width and layer thickness (all of them in cm), and then dividing the result by 1000. Then multiply this liter amount with 1.6 kg/l (the approximate bulk density) to get the required amount in kilograms, referring to dry sand. These data refer to quartz sand; garnet and especially basalt sand are heavier. You will therefore require more weight for the same layer thickness.
Dr. Bodo Schnell