crushed oyster shells for substrate?

[Cichlid Kid]

A friend of mine recently moved to the other side of town and said his tap water ph is around 6.6 - 6.7. He was wondering if he could use crushed oyster shells instead of crushed coral because its alot cheaper. I told him i didn't see any reason why not as it should buffer about the same as coral.
I am by no means an expert on this so i told him I'd ask on our forum.

 

[Malawi Freak]

I have never heard of someone using it but I don't think it would be a probably as long as they are properly cleaned before using. Just make sure they aren't too sharp.

 

[Cichlid Kid]

I think you can buy crushed oyster shells at farm supply stores used for a suppliment in chicken foods for egg laying?