Hi
this is my friend's tank , he imports fish from Thailand , so the discus (leopard snake skin) and motoros are from there .
its not a fancy tank ,cause these rays offered for sale soon after they arrive
he has a sump and also he uses ozonizer to improve water quality (he feeds them well cause they arrive skiny)
i dont exactly remember the footprint , but i think its at least 4*4 ft.
you can get a sense of the dimensions on this video (don"t worry about the smaller speciemen ,later they were separated):
http://www.youtube.com/watch?v=WVPRx8wrIYQand here are the "Penang eruption" discus
http://www.youtube.com/watch?v=egBOU829izo 
what kind of rays and discus are you planing to inhabit your tank?
personally i prefer wild discus
.
it would be interesting to see some images of your new set up .
good luck
