Crushed Shells, Uses?

[Delphinus]

Actually I'd even be a bit leery about using them in a calcium reactor. We have no idea how much phosphate is bound in those shells. It might be fine but there's no "control" so to speak.

I went through a phase of using oyster shells as mountings for frags. It kind of worked but I just couldn't get past the "it looks like a frag glued to an oyster shell" thing -- it just didn't look natural and I gave up on it. Not that frag plugs look much more natural. I guess my mistake was just using the shells as-is, not breaking them into smaller chunks (actually I think I did try that, it's just that when you break the shell they tend to disintegrate .. also an oyster shell that's 1"x1" square may not be heavy enough to hold in place in the current).