Stray current

[Nebraska_cichlids]

I never worried about stray current caused by aquarium equipment, until I replaced a heater the other day. Later that day, the fish in the tank were not feeding well and just hovering at the bottom of the tank. The temperature in the tank was the same as before. The next day the fish were very lethargic. I picked up a new heater and within hours the fish were back to normal. I did not measure the current in the tank. Did other forum users ever encounter anything similar. By the way, the name of the manufacturer of the faulty heater starts with an A.