These little plastic bio balls have loads of surface area for the growth of bacteria for filtration. There are approx. 84 bio balls per gallon. They are used as the biological media in salt water and fresh water aquariums as well as ponds. They are really simple to use: place into a mesh bag and drop into the pond filter. Do not clean the bioballs once they are cycled, or you will risk killing off all the beneficial bacteria that you need to filter your water. Another use for bioballs: fill your tank's overflow box. It will quiet the overflow greatly. and keep out
the snails the box size is 12''x 12'' x 5 1/2''