My Nerite snail in my 10 gallon Betta aquarium feeds off the algae on a thin piece of driftwood and on the glass. But he also seems to eat some of the wood too as seen by a big gouge in the wood. Is this normal for a Nerite snail? Is there much calcium in wood. I do not add any calcium to the tank. Hardness is around 175ppm. Nerite looks very healthy with a nicely colored striped shell.