i've used windex for years with no issues. the only real problem with it is that it streaks salt like crazy. so i usually wipe down with some RODI water to get up the salt creep, then dry towel, then spray the windex on to the paper towel, facing away from the tank. wipe down, and sometimes i hit it with another dry paper towel, just to clean up any streaks left behind.
that is, of course, when my lazy butt actually bothers to clean the glass.