I took ages trying to find a suitable substrate for my rays. I wanted fine, smooth, attractive gravel which the rays could bury into, wouldn't stick to or harm them, and wouldn't get into my filters! Eventually decided on Caribsea "Peace River" only to find that it's not available in the UK
In the end I went for a sugar-grain size river sand that my LFS was using for their long term rays which were looking very clean and healthy......only thing was that it's sold as silica sand!
In fact, when i handled the sand it felt smooth-ish rather than too abrasive or sharp and it seems to be working out OK......apart from the fact some of it still ends up in my filters settling in the bottom of the canister. Never reaches the impellers though. 
In the end I went for a sugar-grain size river sand that my LFS was using for their long term rays which were looking very clean and healthy......only thing was that it's sold as silica sand!
