Does anyone know what this might be?

[*SENSI*]

i got this several months ago an put it in the QT with something else, well got to looking around an saw it but i cant remember the name of it or what it is an i cant find it on any of my receipts?? But im talking about the reddish orange flat thing in the middle of the pic

anybody know???, And is that a good place to set it or do i need to pick a better place or position? thanxs Mike

 

[Reefs-A-Lot]

looks like an orange/red montipora cap. under LED these should glow orange like a highlighter.