3 bucks is a steal, live or not. IMO
, get all that he has, then maybe a few pieces of more expensive rock with life all over it, and wait for it to spread. If its "ultra cured", meaning there is no die off or bacteria, you can always cycle the tank with a raw shrimp.
Dead rock will get all the good living stuff on it over time. It may take a while but it'll happen eventually, as long as you add in good rock for it to spread from.
And like roka said, if you notice an ammonia spike then its still got bacteria on it.
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