i think Rallyman brought up a excellent point about using a UV. i do know a lot of ray owners that use them,however if water is to sterile maybe fish can be more susceptible to getting sick. i was talking to my LFS about getting me a UV for my 300 gal his thoughts were like Rallymans about there immunity system being to week with a UV.i don't know what the best filtration is for rays i suppose if something is working well for you then no reason to change it.
John