I am in the beginning stages of setting up a mbuna tank. Currently scrubbing and cleaning some rocks i got from a local landscaping place for free but these rocks seem to be leaking dirt or some other substance no matter how much i keep scrubbing. I tried pouring some vinegar on them and they dont bubble but I am not sure if they are safe nor do i know what type of rock it is. Do these seem safe to you guys? Any advice would be appreciated.