This heater is compact compared to an adjustable heater. When heating up, it only turns on for a few minutes so that nothing burns through. The sizing is not correct at all. This is part of the problem with the preset. Although it should heat up to 78, it doesn't. 50w heats up to 74 and 100w heats up to 76. The tank is a 5 gallon Fluwal Chi. This is the reason for 4 stars. The heating itself is good, but does not heat as it should. The temperature in the aquarium is measured with a glass thermometer, so there is hardly any room for error. The reality is that for small tropical fish, 76 is in the safe range.
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