1
I think we all know this but just in case here is a nice article explaining why not to.
http://blogs.discovermagazine.com/notrocketscience/2011/04/05/world%E2%80%99s-2nd-deadliest-poison-in-an-aquarium-store-near-you/#more-4232
http://blogs.discovermagazine.com/notrocketscience/2011/04/05/world%E2%80%99s-2nd-deadliest-poison-in-an-aquarium-store-near-you/#more-4232