Although an economical and compact tank heater, I have found that the 25W model is insufficient to reach the target temperature (72F) in my 5-gallon open-top tank. Ambient temperature in my house is about 60F in the colder months and it only manages to reach 69F. I am concerned that means the heater will continue to run while never reaching 72F.Additionally, I found the power cord to be fairly short.See full review