Have a look here:
www.thebts.co.uk/old_articles/substrates.htm
at what Richard C. Gallon has to say on the matter.
I'm thinking Coconut choir is ideal as a default substrate, but seeing as your GBB (chromatopelma cyaneopubescens) does not have fun humidity requirements and will web up the lot anyway it might just work.
All sand is not equal however. We know coconut choir is ph neutral (supposed to be) with no interesting elements and we know what can live in it and how to deal with it, I would personally stick to what I know and what works when it comes to my precious spider.
So,the spider should web it all up anyway, so it would make very little difference aesthetically and I know the coconut stuff is 100% safe.