Aquarium gravel can play an important role in maintaining the habitat that is your fish tank. It can be used as part of the filtration system, as a nutrient rich substrate for plants or to change the properties in the water. In most cases however it is there purely for decorative reasons. People like to see a gravel bottom because it makes the tank look better and often offsets the colors of the fish. It also provides the fish with more things to do which makes better viewing for the Aquarist and his/her friends.

The type of gravel you want in your fish tank is also determined by the type of animal and plant life that you want in your tank. If you are looking for gravel for soft water this is generally because you have fish that are suited to soft water. Common fish include South American Cichlids like Discus and Angel fish. You may also want to have plants in you tank to recreate the natural environment of these fish. Then the gravel must be rich in nutrients and be firm enough to allow roots to take hold.

The gravel commonly used for this purpose is titled lime free gravel. Lime or calcium carbonate is the principle component that causes hard water. If you were to put gravel that was composed of calcium carbonate in then the water it would turn the water alkaline over time and could cause stress or ill health to your fish.

Lime free gravel is usually quartz or man made. Quartz gravel is ideal for plants as it collects nutrients and allows roots to take hold. You can also layer the substrate so that the base is lime free material and the top levels are more nutrient rich to encourage plant growth. Another consideration if you have bottom dwelling fish is to have smooth edged gravel so that the fish don't get damaged.