Sorry, just got back from holiday. Cant find my previous infos, here's another link about some tiles talk.
http://www.monsterfishkeepers.com/forums/showthread.php?t=258949&highlight=tile+bottom
Sorry to get u jumping! lolz I remember reading somewhere that some types of tiles releases chemical that is not suitable for fishes. Let me track back my re-search and post the infos.