Usually when I see spots on the leaves like that they are more of a rust colored and I consider them to be calcium issues, you're in hard water so that probably shouldn't happen. Those spots also look a little bit more black than what I would expect.
Are you seeing these only on your lower leaves? If so just a general increase of feed might be all that's needed.
With mother plants it's perfectly all right to cut them way back and let them build themselves up again. Then cut them back again and so on and so on....
J
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