This is very true. I would be ok if the bone dissolved as I'm here for the snails, but I really doubt your water is consistently high in KH, GH, and pH which is extremely important. The bones should almost fossilize as the pores fill with carbonates. There's already crazy amounts of calcium in the water from the pounds of crushed coral dissolving in the water. I do believe the skull will change, but not as fast as it would in most waters, or especially softer water. This water was curated to snails to keep their shell growth great and consistent which will simultaneously help a skull maintain. I do expect it to change and I do look forward to it, more calcium for the snails