Somewhere just the other day I read a discussion on here where someone said that the red grit contained iron which gives it the color, but I can't remember where I saw it!
I offer both in a mixed container and when I need to refill it there's usually an equal amount of grey and red left meaning mine don't seem to have a preference.
I offer both in a mixed container and when I need to refill it there's usually an equal amount of grey and red left meaning mine don't seem to have a preference.