First of all... What is your pH? How long have you kept fish? And how much time do you devote to your tanks? What size tank do you have?
I ask these questions because Freshwater stingrays are very delicate, and will die quickly if not cared for correctly...they are also around $80-$100 in most stores, and the store prolly won't let you buy it, unless you have the right tank requirements... Get back to me.