I don't know why the Hart isn't sharpening up for you, but I agree with the advice not to get another hone. If the progression you have (I use the same progression) isn't working, adding another hone into the mix isn't going to help. If nothing has occurred to damage the bevel, all the blade should need is a refresh. If you're resetting the bevel, that happens at the 1000k level. The only benefit to going beyond a 12k is to refine an already perfectly set bevel, which doesn't seem to be the situation here. You are perfectly set up with the stone progression that you have. I would advise working with a mentor. Good luck.
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