I bought a used 75 gall RR Tank from my LFS. The tank came with substrate already in the bottom. My question is " Is it safe to use"? I am concerned that the previous owner may have had something in the tank that i might not want in mine. For example, disease, pest algae, chemicals, etc. I have had the substrate drying for some time now so it is not wet. Am i overthinking it and should feel safe to repurpose some of the old material with a decent tank cycle or should i scrap it and dont tank any chances and just buy new?