They definitely need rinsed off and cleaned first, water only and/or vinegar. Then take each individual rock and drop vinegar on it, if it fizzles/bubbles I wouldn't use it it will mess up water chemistry but if it doesn't fizz it's fine to use. Next step is boiling/baking them to insure nothing harmful is on them but because this is quite dangerous if there are air pockets, what I did was put them all in a 5 gallon bucket, boil water then pour it over them and put a larger bucket on top of that one just as an extra precaution. Did this twice letting them soak for about 6 hours each time. Never have baked them so don't know much about that area. You could also bleach them instead of boiling/baking but it will take a while to get all the bleach off the rocks and make them safe again so I'd recommend the pour boiling over way. It's really just rinse/wash → check for fizzles with vinegar → boil/bake/bleach to sterilize → short rinse with water → add to tank
