im selling the fish out of my 180 gallon tank and im thinking of getting a stingray for it but i have never kept any rays before any advise would be great also what should my tank have in it as far as substrate goes it has smooth river stone in it right now would that be okay its about the size of a peanut and smaller would that be okay for a ray? also i have three 6 inch clown loaches would i be able to keep them in the tank withe the ray?