Pumiice stone or calcium eraser? Will those scratch the tile? I do want to remove the ring but dont want to disolve grout or scratch tile to do it. These has to be a not damaging way to do this.TA 60-70.
I consider a CSI of 0 to -0.3 ideal. Aim for that range. To lower the TA you might end up with a temporary CSI that is very negative but that is unavoidable and will not cause damage because it is short-term.
The acid will dissolve some of the grout but if you want the ring gone, the only other option is a pumice stone or a calcium eraser.
Far easier than any of that is to prevent it from forming in the first place.