Add a bit of vinegar with water into one of those spray bottles, spray on glass and wipe with a piece of newspaper. Never leaves a streak and safe for the fish.
We used to use this to clean the glass display cabinets for cakes in a cafe.
I will try some of the alternatives posted here, and use the other stuff for cocktail mixer for people I don't like. Hey Rally, would you like a Mojito? J/K