Hi all. I am working on rehabbing a 135 gallon tank that has seen it’s better days. This tank had calcium deposits on it when I bought it. I have been trying to clean these stains for some time now and am at a loss. I have tried everything that I know multiple times. Every time cleaning I would make a little progress. But the last several times I have seen little to know progress. What I have tried: vinegar, razor blades to scrap, Keepers Friend. I have tried these seperate and in conjunction with one another but progress has stalled. Any suggestions would be appreciated. I will attach a picture for your reference. Thanks. 