swiffer!!!
just kidding, i actually just use spit.
i'm being serious. i clean it a couple times a day and i usually just wipe off anything obscuring my view with a wet finger.
as far as deposits on the frame i use a toothbrush and tank water.
it makes for a lot more frequent cleanings, but i'm all over it anyways.
windex will be absolutely fine as long as you spray it onto your wipe off media and not the actual tank. overspray is what you want to avoid. the best wipe media is actually non shiny crumpled up newspaper. spray a couple squeezes and wipe. try it on a window if you want to experiment. newsprint doesn't leave the fuzzies like everything else.