A pair of fan coral skeletons that could be used as decor in or out of a tank. These could be added to a marine tank or used to add an alien or unnatural contrasting appearance to a freshwater scape. These pieces will undoubtedly offer a ton of surface area for beneficial bacteria to grow and will also very likely leech minerals into your water, which could support invertebrate health. These pieces have been unused for 15+ years (details below).

Disclaimer: 

This used to be part of a marine tank it could still have aragonite pieces, salt crystals, and/or old silicone imbedded in it. I will clear off as much as I can, but I make no promises it will be 100% pristine.

Where it's from:

This piece of lace rock comes from the hardscape of a built-in marine tank that was part of the house my father-in-law used to own. To my knowledge, it hasn't been part of a marine ecosystem for 15+ years. Two years ago, when my father-in-law was selling the house he asked me to tear down the scape. When I got home I soaked it in tap water for a few days, then vigorously hosed it off 2 or 3 times. It has been dry and awaiting use since then.