Can anyone id these rocks

[COCOBBALL]

So i made a purchase of some "coral rocks" and im not really sure what i got. The person selling to me was unsure as well. I paid $30 so i think i did ok.. i got a 100g tank full of it and the tank.

Any idea what it is?

Why is it top flaking off and so crystallized..is it salt?

 

[Flippers4pups]

So i made a purchase of some "coral rocks" and im not really sure what i got. The person selling to me was unsure as well. I paid $30 so i think i did ok.. i got a 100g tank full of it and the tank.

Any idea what it is?

Why is it top flaking off and so crystallized..is it salt?

Not sure, but I would consider acid washing these in muriatic acid. They aren't very porous.

They look aragonite based, but either were used and at one time were covered in coraline or just dry rock never used.

My concern would be leaching phosphates.