Fired it up again after many months of winter to find the water level sensor failing low so it didn't stop pumping until timing out & shutting down.  The electrodes were once again eroded & covered in goo. 

The normal practice was to leave it on after the pump timed out, but it doesn't turn off the electrodes.  When it was left on all winter, the electrodes continued electrolyzing & there might have been enough water to barely touch the electrodes, causing them to erode even though it wasn't pumping.  It should turn off the electrodes when the pump times out.

The longer term solution might be a floating sensor.

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35% proved to be the maximum humidity it was worth running at.  Summer 2023 had no major heatwaves & no humidity low enough to run it all night.  Humidity only got below 35% on a few days, then recovered to 40% every night.  The pump needed another tube change.  The sensor still got a coat of slime & algae.