Most stones are compatible with water features but care needs to be taken with limestone and similar types, because these stones are subject to erosion by water. Stone and gravel inside the lining of ponds help to build the ecosystem — useful bacteria grow on the stone. This helps to keep the pond clear.

Fish, plants, stone and gravel are all necessary to a balanced ecosystem, just like a natural pond. Limestone can negatively affect the pH balance of the water and in some cases affect the health of fish, although some specialist fish may require the conditions produced by lime-rich rocks. Limestone may also make the water appear cloudy.

Serious fish experts recommend scrubbing and boiling all stone and rock before adding the material to the aquarium or pond. This will kill any harmful fungus or bacteria.  To test a particular rock for lime contamination, immerse in distilled vinegar or a dilute solution of sulphuric acid. Lime will fizz and cause the solution to become cloudy.