The depth of gravel in an aquarium will often be based on aesthetic preference. Though gravel levels can range from nothing to quite a few inches, two to three inches usually provides the most visual appeal and is the most practical. More gravel is harder to clean and less gravel makes the tank look empty and will cause fish waste to be more obvious.
Gravel Depth for Plants
Tanks containing plants will need the correct amount of gravel to support the roots. Plants with shallow roots won't require much but plants with deep roots will need two to three inches to keep root systems from becoming entangled or suffering from lack of nutrients.
Two to three inches of gravel is recommended for visual and cleaning purposes. This depth also provides support for even the most deep-rooted plants in an aquarium.