Decorative fish gravel is used in aquariums for a number of purposes. It is, of course decorative in its own right. It can be natural in appearance or it can come in bright, even neon colors. It can compliment the color of the fish or the decor of the room the aquarium is in. Tastes vary.

In addition to direct decorative effects there are indirect effects that enhance the appearance of the aquarium by hiding waste products and excess food. Gravel can also be used to anchor underwater plants to the bottom of the aquarium. This allows roots to grow in the substrate for rooted plants and it allows the fishkeeper to cover the uglier aspects of bunched (non rooted) aquarium plants which are often held together with rubber bands or soft lead bands.

Decorative fish gravel can also serve functional purposes. Part of an aquarium’s upkeep is the nitrogen conversion cycle by which bacteria break harmful waste products down into less harmful ones. One type of filter called an under gravel filter makes use of the flow of water through a substrate of small grade (1 - 2 mm) gravel. Since the gravel is small there is a lot of surface area for bacteria to live on. As the water flows through the gravel the bacteria which are living on the gravel break down harmful waste products to less harmful waste products. Another practical use of decorative gravel is to raise the pH of the water. Some species of fish require a pH higher than the normal 7 of most tap water. Certain types of rocks and/or gravel leach chemicals that raise the pH. Driftwood or boiled sphagnum moss is used to lower pH for fish who prefer that environment.

The breakdown of the waste products hidden by the gravel is not enough to maintain the aquarium, the waste products must also be removed using a gravel vacuum and partial water changes of 10% to 25% must be done periodically. The decorative gravel only hides the waste, it is still there contaminating the water.

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