[flamingo]

I personally used Black Tahitian Moon sand with my small retic. Overall, this type of sand is in 70% of my tanks- and with the ray, it seemed to like it. Allowed it to bury itself easily, was easy enough to "sift" around in, etc.
I remember talk about black sandblasting sand (I can't remember the type) that seemed to be perfect, look great, but was almost impossible to find.

And, with what Gump said, don't really worry about your pH- unless it's ridiculously high. Most species like slightly acidic water, but it's not something you need to stress over.