yes,u r correct.they use it as bio rings or more clear ceramic rings which serves as a medium for nitrosoma bacteria to grow which can convert harmful nitrates and ammonia into nitrites which are nearly harmless to a fish but,i would personally suggest using those bio rings as they are porous and provide more surface area for bacteria to grow on and provide a helping hand to us and u can also place those older rings into new tank if u don't have time to cycle it,it will save the whole time of cycling and fishes will do same as in cycled tank so no harmThanxCK