The problem with covering crushed coral with sand is that the smaller grain size particles will make their way to the bottom and the crushed coral will end up on the top again. Best thing to do is take out the CC and add the sand you want. My suggestion: if your tank is small go with the arag-alive
http://www.premiumaquatics.com/Merch...ode=Substrates
If you have a big tank it will be too expensive to do the entire thing with arag alive so do most of it with special grade reef sand and a few bags of arag-alive
http://www.premiumaquatics.com/Merch...ode=Substrates