My choice for the Visitherm heater was a result of reading the Practical Fishkeeping group heater test which gave this a very high rating. After a month of using this, water temperature has been constantly on about 24-25C. The only gripe is that I should have bought at least 150W for my tank (75L). I think the 100W  takes just a little too long  for the temperature to reach the set temperature during a water change. I should have followed the manufacturer’s instruction that 100W is for tank up to 65L and 150W for up to 100L. Nevertheless, it is working and