Review on YukiHalu Small Size Submersible Aquarium Heater: Accurate 1℉, Mini Fish Tank Heater 50W 100W with Thermometer & LED Display by Rodney Shepherd

In short, luckily my betta didn't freeze. I used a 50 watt heater for my 3.5 gallon pool. In the beginning it worked very well! I was impressed and would probably even give 4 or 5 stars. I liked how accurately it keeps the temperature, that it's possible to change the temperature, and the built-in thermostat seemed handy (it worked for me for exactly 3-4 weeks). Although the glowing temperature gauges on the screen in the water could almost double as a night light for the room. Not being able to turn off at night can be annoying. The fighting spirit is generally light and I suppose this bothered my fish. Now for the real issues: my betta once burned his fins getting too close to lean on the heater when the heating element was fully on. So you should always try to slowly increase the temperature of the water with it, so it was partly on my side, but I didn't expect it to be that strong. Then, after a month of good and "bright" service, his thermostat began to fail. It showed slightly higher than the real numbers. I noticed something was wrong and started comparing the accuracy of the readings to my old thermostat (never had to take it off!) so I gradually increased the numbers to keep the temp at 78F. For example: real 77F water showed 79F on the screen so I set the temp to 80F or 81F and so on. So the actual temperature stays at 78°F. This helped stave off the problem for a while, but the actual water temperature dropped another degree every few days so I had to adjust the thermostat to compensate. After about two months, this heater failed completely, it no longer heated any water at all, even with the thermostat set to the maximum. Conclusion: I no longer get too carried away by heaters. I now have a TopFin 20W heater and it is perfect for my pool size, has lasted longer and is cheaper. My 10 watts weren't enough for 3.5 gallons in the winter.