Just give them a good bleaching first, soak them for awhile, use activated carbon in the filter, do lots of water changes, Deer antlers, cattle skulls, etc, all have been used, but not much.

Would seem well suited to piranha tank though.

Looks like a good start and youi are thinking about different ideas, that's good and the site and club look like it's off to a great start.

Regards,
Tom Barr