I was recently given a 10 gallon tank setup that had been is storage for who knows how many years. The tank is covered in calcium. My son and I spent all weekend cleaning spare tanks, decor, gravel and rocks that we had acquired over the past couple weeks. We thought we had gotten the tank all cleaned up until it started drying and we saw some calcium we missed. Anyways, I have used diluted vinegar, straight vinegar, scrubbed and scrubbed some more I even used a razor blade and that didn't touch it. Any ideas on how to get the stains off? Wouldn't be so bad if it wasn't right in the middle of the glass.