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?

Not sure if the calcium would dissolve very readily from the eggshell just floating in the water?
I did have a broken egg, empty inside, small hole on the top side, just smaller than a chicken egg floating in my pond yesterday. I'm hoping it is a left over snapping turtle egg and not the result of a raccoon raiding our mallard nest on the edge of the pond. I should have left the egg shell float in the pond and see how long it takes to fall apart?

Unless you eat enough eggs daily to run your cholesterol over 1000, I doubt you could notice any difference, good or bad.