A 180 will eventually be on the small side for both the shark and the ray. The shark will outgrow the tank first, probably within 3 years or so. A baby ray could probably go 4-5 years in a 72" x 24" tank... assuming it survives. As the previous poster indicated, use fine sand and minimal rockwork, (though the shark will need at least one good size cave to hide in). If you have specific questions about feeding, tankmates, filtration, etc, that would help. Good luck.