Cloudy residue at top of tank

I'm assuming your talking about hard water deposits on the sides of the glass? Having recently acquired and restored a handful of used tanks I found that even white vinegar to be ineffective on our old, caked on hard water deposits. My solution was some strong fingernails chipping away at the deposits after wetting them with something. I used the vinegar on empty tanks but simple tank water if they are already filled. Something sharp like a butter knife will work but will scratch your tank. Does anyone know if they make any kind of plastic tool that may do this job without scratching the glass?

The best solution I found is preventative. Keep your tanks filled so the top water level is behind the top frame of the tank at all times so any deposits from the top water line is out of sight behind the frame. Especially during the winter when the air is so dry I found I can lose water level very quickly. Any tanks that don't have adequate covers, I'm finding losing water level daily this winter and I'm topping off with water 2 to 3 times a week to prevent the mineral build up.

+1.

Only way to remove it is to empty the tank.

This solution will require emptying the tank if it is not already empty. Vinegar is usually pretty good at removing the build up. Just rinse it real good after you are done cleaning.

Anyone have any ideas on how to remove a cloudy build up of some sort at the top 6" of my tank. I would guess its mineral deposits of some sort as i have my filter returns blowing towards front of my tank. Razor blade didnt seem to remove it. Any help would be greatly appreciated.