stingray

What is the minimum tank size/dimensions for 2 teacup stingrays? Also, what can they be put with? Thx!

Hey guys, I'm relatively new in the stingray hobby and was wondering if sand changes any of my waters parameters besides the obvious cloudy water. And also if it is safe to add to an already up and running aquatium with rays already in the tank. Of course I was gonna rinse the sand like a mad...