Hate to ask a stupid question but, been have thinking of this for years, so here goes.

Are there any benefits or drawbacks to adding eggshells (chicken eggs) to the pond?

The thought of benefits are motivated by a few things, shells are mostly calcium and we know ponds need some hardness or calcium to be healthy. I recall my grandma used to put crushed eggshells in the garden to help increase calcium to the veggies, at least that was the explanation. Another is, in a pond that is mostly a mud bowl, would the shells offer some sort of terrain, that the fish might benefit from?

As far as drawbacks, I wonder how long it takes the eggshells to start the breakdown and give up the minerals, would they ever breakdown at the bottom of a pond? Any others???

Obviously the mucus portion of the eggshell might bring unwanted results so, a rinse and a week in the sun, before introduction, might be in order.

Pond experts, what say you?