I was very excited to use this for my Betta. I got it all set up and followed the manufacturer's instructions to a T. It took 24 hours to start working, which was fine and to be expected. It kept the tank nice and warm for another 12 hours and then stopped working. It still isn't working, light won't turn on and no heat from the device. Aqueon customer service was not helpful... she told me "honey, water feels cold to humans..are you sure it isn't your thermometer that's broken?" Chewy was a different story. I let them know it wasn't working and theh sent a replacement right away. Great customer service.