I would first recommend doing a good amount of research.
With rays, knowledge and dedication are key and it is always best to know what you are getting into before getting your feet wet.
The stickies above this forum are a great place to start.
There are also a few really great books out there as well.
One is by Dr. Hans Gonella & Herbert Axelrod. The other is a Barrons book.e
Both are a great read and will answer many of your questions as well as arise many new ones.
All Potamotryon, Plesiotryon and Paratrygon inhabit strictly freshwater.
For the most part you will probably be dealing with Potamotrygon.
The Himantura and Dasyatis species are another story. Himantura inhabiting both fresh and brackish waters. Dasyatis are stricly brackish/saltwater dwelling for the most part, only wandering into freshwater for short periods of time.
I would do the research first and then decide from there which ray would be best for you. For rays, dedication is key. Regardless of how big they grow or what size tank they need, they all demand a great deal of attention (A few moreso than others). But dedication for all rays is key as I mentioned above.
Ray keeping is a passion like no other. Good luck on whichever you decide and remember that you can always ask questions on here when all else fails.
Keeping rays will change your life. They are infectious to the heart and grow on you very quickly.
Highly recommended over dogs, cats, children and all other animals
