Aquarium Filter media (used in filtration pumps to keep aquariums clean). It is generally advisable to change filter media between 12-18 months to ensure filter pumps perform optimally. These little plastic bio balls have tons of surface area for the growth of bacteria for filtration. Do not clean the bio balls thoroughly, or you will risk killing off all the beneficial bacteria that you need to filter your water.

Note:

• They are really simple to use: place into a mesh bag and drop into the pond filter.
• Another use for bio balls: fill your tank's overflow box.
• They will keep your snails and other animals from going down the overflow as well as quiet the overflow greatly.