There are many types of rocks you can use to anchor a pond liner and disguise its appearance. However, this cover material for a pond bottom still has a few issues you need to address before using it. First, make sure to choose smooth and rounded rocks rather than sharp edged chunks or gravel. The weight of water pressing down on the rocks can cause sharp edges to dig into the material and cut or stretch it. Second, consider the cost of rock and transportation fees before choosing it as a pond fill material. The weight of rock makes it ideal for holding down liners that rise from ground water or gas pockets, but you’ll need a thick enough layer to prevent bubbles from pushing up between pieces.
Rock is a good way to encourage clean water in the pond because the openings between the rocks foster healthy bacterial growth. These bacteria eat the waste of fish and broken down plants that would otherwise become a thick sludge that releases odors. Yet some amount of sludge will accumulate no matter how much beneficial bacteria you have. When it’s time to remove the sludge, you’ll find the rocks complicate this process by making the surface uneven. Consider the trade offs for this material to decide if its right for your pond.
