Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Many different rocks are called 'Slate'. If it is fairly hard and can be cut into thin pieces it might be called slate.
Real slate, the original material is aquarium safe as long as there is not a lot of minerals in it. I have seen some slate that has quite a bit of iron. If the slate has rust spots don't use that one.
The other rocks that are cut into slabs like slate and may be called slate should be tested.
If you want to sterilize a rock you can use bleach, rinse, then use dechlorinator. Standing it out in the sun also gets rid of chlorine.
Rubbing alcohol is another way, and it also evaporates.
If the rock came from a wet location, this might be a good idea, but I do not do this for rocks that come from dry areas like rock yards.