bleach it for 2 months in a tub with water and a gallon of bleach. dump the water out and fill again with clean hot water and water conditioner\ declorinator. let sit for a few more days then let dry in the sun for a few days. this will get rid of all the death and make them new again. i wouldnt just put them into the tank it might send it into a cycle and spike the nitrates. they look pretty dirty and *****
You dont want to do that. Put it in a tub with water and flow for a month doing regular water changes and tests. You put it in a established tank you may end up with a cycle.
This rock came out of this tank just allowed to dry. I wasn't sure about using it since I had enough coral/live rock to replace it with. I'm not sure what this is but I think it's lava.
i got about 75 lbs of dry rock from someone on craigslist and he said it would be fine to just add it right in. i cycled it and am i happy i did. if i had not cycled it, it would have nuked my tank. better off safe than sorry.
I could bleach it for a few days but this has been my rock. I think my main concern if the rock itself could be a hazard. Like I said it was in my 55 marine tank and when I upgraded tot he 100 gallon I got enough coral rock to not need to use this but now I want to use it because of the shapes.
If it came from another tank it will have die off, etc. So I would not put in an established tank. Either cycles by itself or do one of the bleaching methods already stated.