Almost killed the tank!!
It was a super busy weekend for me, and I rushed cleaning the skimmer.
Well, I accidentally knocked a plug out of the relay box.
Put it back in without thinking much about it. It is labeled, but I did not check carefully.
I ended up putting the top-off pump into the currently unused fuge light plug.
Fuge light normally runs 12 hours, during the night.
OOPS.
Fortunately, the pump is rather loud, and I heard it late at night, thought that was strange, so checked.
It "only" pumped about 5 gallons of fresh water into the system.
But if left running overnight.....
Fish might have survived the low-salinity, but not the corals.
Those multiple float switches as backup did no good at all. The micro-controller though the pump was off.