Substrate of Corys

I have my panda cories on gravel, and their barbels are at least a third again as long as they were when I bought them a year ago. I think that it's the quality (smoothness) of the substrate that matters, not so much the grain size (within reason, of course). I'd imagine that smooth gravel would be better for them than sharp sand, and smooth sand better than sharp gravel. Just my opinion, YMMV.
 
Thanks All....your help saved me from making the wrong purchase and put me on to a more appropriate product......
 
AquariaCentral.com