I have a 46 gallon with a glass hood. Over the past 8 months I've
noticed that the hood has accumulated some mineral deposits, mainly
near where my airstones bubble air up the surface. I'm guessing it's
because of water splashing onto the glass, evaporating, and then
leaving the minerals behind. It's actually quite a bit too, I'm
guessing that's because my tap water is pretty hard (GH btwn 150-200
ppm), and the fact that I rarely clean the back part of the hood.

Is there a safe way of cleaning that stuff off the glass? Using tank
water and a scouring pad won't even remove all of it. I thought maybe
about using some kind of vinegar solution, but since it sits so close
to the water, I was worried that that might contaminate the water.
Any good ideas?

Sorry if this is a dumb question, but I'm a newbie and don't want to
screw up what has turned out to be a nice little tank.