depending on what is in the tank it could really cause problems. the longer the bone is in water the more it will break down. it could take several years to do so but as it does it will leach calcium into the water and alter the chemistry of the tank. if you are really set on doing this boiling is good. i would then let it air dry for a while a couple weeks or so to make sure it was completely dry all the way though. i would then find a clear acrylic spray and seal it several times.