is out of the water for any period of time there is going to be some die-off of the organisms living on/in the LR
. That dead material will decompose causing the release of ammonia, etc., etc.
If it's out of the water for any log period of time you can test it in a bucket of sw
as suggested. You can also cure the LR
in a tub for a few weeks to let a cycle complete, and then transfer it to your tank.
If bringing if home from the lfs
, find out how long they have had it in a curing tub. IF it's been there for weeks+, then bring it home wrapped in wet towels in an insulated box to prevent as much die off as possible.
If you are only adding a few pounds of new LR
then you SHOULD not have any problems