Tank temperature plummeting

[GaryE]

Heaters often fail. So do thermometres. I think you have had both.

If it's goldfish, they shouldn't have heaters anyway.

 

[Ram419]

Those are also handy during water changes. I also use mine when preparing water to hatch baby brine shrimp.

Yup, that is what I use it for primarily. Usually the water is too hot so I throw ice in the bucket to cool it down. Using the infrared thermometer to adjust until correct temp.

 

[AlexT]

maybe the aliens abducted the fish tank and chilled the room to hide the heat signature of their ship from the US government

Something fishy going on