DO Rocks have good bacteria, like gravel ?

[Joeybsmooth]

I was told that I should not just change all my gravel since it haas good bacteria inside. Can the same thing be said for rocks. They are like the size of a marbles? I did not know if it was difference since gravel is so fine.

 

[jetajockey]

anything that has biofilm on it holds bacteria. A porous rock like lava rocks actually make good biomedia, a more solid rock would still have some, but not nearly as much.