shells getting holes

I have noticed on a couple of shells (just a couple), that there are holes developing through the shells.

Is this normal?


One shell is a rather large one (fist sized) that I have and am using to redirect some water flow. The other is from the very first hermit I put in tank (survived the cycle). Its shell is unique to the rest and I can easily pick it out. It has holes all over it (has been unoccupied since it started getting holey).

The rest look fine. My Mg/Ca params have been overall steady but dipped a few weeks ago for a week and are now back up to par again... so I don't think it's a lack of Ca causing this... though the thought did cross my mind.

Any thoughts?

 

A few of the scattered ones I have had for a while do it too. So I would THINK its normal
Just randomly guessing, that all the shells really are are calcium. And since there is no living snail there any more to regenerate it, they slowly dissolve?

 

That makes sense. Unfortunately, it was my favorite shell. Since it was the first hermit, whatever hermit that happened to be inhabiting it, was my favorite.

Now they're all just crabs :

 

Mine do it too. I think it's just the calcium carbonate being dissolved into the water.

 

Any rocks in the ocean will slowly erode/dissolve. That is why corraline algae is such a huge player in reefs- it protects them from eroding due to ocean currents and also aids in protecting it from dissolvement (actual word?). Also probably why it was the first technical coral ever- it was the building block for which all other corals could inhabit the rock.