Choosing the right aquarium gravel is actually very important because you have to take into consideration the particle size and type of material of the gravel. If the particle size is too big, pieces of uneaten food and solid waste will get trapped in between and thus will accumulate there. Soon, it will start to decompose and releases toxins that will cause changes in the aquarium water chemistry. Bigger sized aquarium gravel will also unable to provide good anchorage for the roots of live aquarium plants. On the other hand, if it is too fine, the gravel bed will become too compact and chokes off air and water circulation through the gravel. This will cause plant roots unable to perform respiration and debris that gets trapped among the tiny space will rot and accumulate noxious gas especially ammonia that is harmful to the fish. Depending on which types of aquarium fish, fine sands will also create problems for certain fish such as goldfish, which will accidentally swallow the sands when scouring for food in the gravel bed.
Usually particle size of around 3mm diameter is the perfect size for use in aquarium fish tank. If you are using the aquarium gravel as filter media, the gravel bed should be at least 5 to 8 cm layer of thickness. If it is only used as a substrate for plants, you just need the right amount to cover and provide anchorage for the roots.
Another important consideration is the type of material for the aquarium gravel. The best selection is to use either stones or granite because both materials will not dissolve in the water and alter pH and water hardness level. There is also another type called iron enriched gravel substrate, which is basically gravel that contains essential nutrient for growth of aquarium plants. Avoid using limestone, coral, cockleshell, fine sand, marble or colored pebbles with paints that will peel off over prolonged period in the water.
Having gravel does have its benefit but one must be prepared to commit more time for the aquarium maintenance aspect. It is important that the gravel must be cleaned at least once in a month by either digging into the gravel bed to siphon out the sediments or another simple approach is to use aquarium gravel cleaner. You have to ask yourself whether you are willing to commit your time doing that and if the answer is no, then you have to resort to having a barren aquarium surface setup with plastic plants or using an overhead filter instead.
Related topic: Learn about Setting up your own Aquarium