Can crushed oyster shell be used as a substrate?

[Aquattro]

Originally Posted by Don E

Don't people use oyster shells as a major ingredient in DIY live rock?

Again, I wouldn't, but some people do. When I bought my 75, the guy had oyster shell as a substrate. Even the fish had cyano growing on them!! Seriously, there was more cyano in that tank than I'd ever seen and he said it started as soon as he started the tank and got worse as time went by.
I can see no reason to use oyster shell; if you can't afford or don't want to use aragonite sand, crushed coral or silica sand are both viable low-cost alternatives. Glass beads have even been used successfully.