I have some similar stuff in one tank, I keep trying to get rid of it but it comes back from nothing every time. I don't know if you'll be able to save the plant, but I would try manually tearing out as much as you can to see if you can get the plant to grow healthy, then you might have to repeat later.
I don't know about Marysville water specifically, but I think with our changing seasons we get a lot of fluctuation in mineral content of the water- especially since it's runoff and not groundwater, since all of our water comes from reservoirs. I have wondered why my tanks occasionally break out with issues like this, and that's what I am beginning to suspect as the culprit. Do you use municipal water?