I got a 75g tank that was used for turtles. It's got some serious calcium despoits on all four sides and I just can't get rid of them. I tried scraping it off with a razorblade, soaking it in vinegar for a day and scrubbing like hell but it just won't budge. If I angle the razorblade correctly and concentrate on one square centimeter for 10 minutes I can get some of the glass clear, but I don't want to scratch the glass and there must be an easier way. Am I doing something wrong here? Maybe not soaking it in vinegar for long enough? Can i use some more harsh chemicals and rinse it thouroughly afterwards?