Bleaching Rocks

[TxBrew]

I just got a new fish tank and have several nice pieces of limestone, around here called Texas holey rock. It looks like this;

I've soaked the rocks overnight in pure bleach but can't seem to get them the really white color I would like.

Any of suggestions on how to bleach these rocks so they are bright white.

 

[SuperiorBrew]

I think I remember reading hydrogen peroxide works on some