I know another slate post. I did search and search and search so more and everyone seems to agree slate is safe in an aquarium bit the only slate I can seem to find anywhere is multicolored. Ive gone to like 6 diffrent places, homedepot, lowes, tile stores none have had just grey slate. I also took a small dropper bottle of muratic acid with me and put a few drops on the slate at each place I went. Every single one would fizz on the colored part but not the grey part. I had a piece of this tile at home and soaked it in an a mix of muratic acid and water for 30min. Then in water baking soda mix for 30min and the rinsed it of and tested it again and no more fizzing anywhere. Sorry long winded, if your still reading my questions are, is this slate still aquarium safe? If not the Since it didnt fizz after an acid bath is it safe then aftwr being rinsed well? I'm looking to make slate caves in my 150g planted tank and dont want to kill everything fish or plants