I've been testing this water heater for two weeks now. At first I wasn't sure if it was working because the display was dimming, but later I found out that it happens when it gets warm. I did a partial water change this weekend and found the light came back on when the water got colder than the 78 degrees I set it to. It also indicates when it exceeds the temperature. This size is great for my Betta's 5 gallon tank. I love that it's fish safe and blends into the background as opposed to the unsightly water heaters of the past.
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