Sand is just one of many materials to cover the bottom of a pond with, and it has its own benefits and issues. Some pond designers and koi keepers feel that sand is always the best, while others prefer gravel or mud. Sand is heavy enough to hold the liner down and prevent floating, even when gas is produced, as long as you add at least three to four inches. Sand is one of the easiest to clean materials to cover the bottom of your pond. It has a smoother surface than gravel and isn’t as loose as mud, making it easier to remove sludge without accidentally getting rid of the sand.
On the negative side, sand doesn’t offer quite the same opportunities for beneficial bacterial colonies as gravel or mud. This tightly packed surface of small particles may be easy to clean and attractive, but it’s lacking the gaps between gravel that leave space for useful microbes. If you’re only using your pond for swimming or plants, you may not care as much as a fish keeper about the bacterial colonies. These microbes are essential for koi and goldfish since the fish produce a lot of waste that needs processing.
