Not maintaining the correct temperature
Make sure it’s been in operation for 36 hours. The heater will slowly raise or lower the temperature over time, which prevents a large temperature swing that can shock the fish. Check your water temperature with a submersible thermometer or, better yet, a strip thermometer that adheres to the glass. If the heater is not working properly, feel free to contact us anytime, or visit your local pet store.
SAFETY NOTE: Never remove a heater from the water if it is still turned on. Unplug it first, let it cool and then remove it.