Doug Kanter writes:

And use quality clear ice, not the cloudy tap-water-in-freezer stuff.

I know clear ice looks better in clear cocktails, but how does the
normal stuff affect a slushy?

Being largely demineralized by the freezing process gives it a mordant
quality that interacts differently with the beverage flavoring, amplifying
it. Hard to describe. Also no off flavors from sublimating in the
freezer.