Ok so here is the story.
CC is made up of CC and shells. Shells are loaded with Phosphate, but that phosphate is locked up in the matrix of the shell, so as long as the shell doesnt melt then the P will stay in their.
So on to your story. When you have an existing substraight you need to stage the extra sediment you put on it. Basically if you dump a bunch of sand onto top you will kill the bacteria and whatever life you may have in their because you will starve it for oxygen. So what you want to do is to add about a 1/2 inch over the whole surface and then wait a few days to a week, and then do it again and so on and so forth until you have the depth you desire. Doing it in a staged manner will allow the bacteria to stay oxygenated and populate the new layer, also any life you may have in their can move up and not get starved of oxygen.
Ok downside of your existing bed. Know the above you dont want to melt the CC. So now with you adding sand on top of it your going to make the area where the CC is anaerobic or devoid of oxygen. This will lower the ph in that area and you will get melting and thus release the P that is locked up in the shells.
good luck
Mojo
