It's not the well water, what you are experiencing is very common on new pool start up when the startup method is standard startup and not acid startup. The bicarbonate startup method, which is the other way to start a new plaster pool, is only suitable for marcite and not for aggregate finishes if I am not mistaken so I am going to assume your builder did a standard startup procedure and because of the scaling is going to do a modified acid startup to dissolve the scale.