Is your GH 30ppm?
If yes, then this is very low (soft water) and there probably isn't enough minerals for a nerite snail.
You can add limestone, shells, dead coral skeleton or coral rubble to the tank and it will add a bit of calcium to the water, but it will push your pH up and that isn't what you want with tetras and Cories.
Cuttlebone is made from the same stuff (calcium carbonate) as limestone, shells and coral.
You could add a small amount of Rift Lake water conditioner, but that will also raise the pH.
I would probably leave it and see how the snail goes. Most snails are fine in soft water as long as the pH doesn't go below 7.0. If the pH does drop, the acids in the water dissolve the snail's shell.