Coffee ? UGH !
when my cell did that it coated the plates real badly and I finally did the muratic acid wash out
to get it back to normal.... but I was using KOH not lemon aid ! ...I know I had some regular steel in my cell at the time ... I wonder if it was the steel tainting the electrolyte

I bet ya dollars to donuts you have some regular steel in there and its the Steel that caused the electrolyte to go brown on ya !
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hope ya don't have to do the acid bath to get it clean again, but it is a bunch simplier than a complete tear down!
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Keep us posted on it please !
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do you have that LED on a thermostat or just a switch ?
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Bob...