Magic warming tank of power + 2?

[Slyspy]

I accidently unplugged the heater on my cycling tank this morning (wrong one, doh!). Found it tonight and the temperature still reads 80F (27C). The tank is a small one (20litres max) and I thought the heat would have dissapated since my room temp is 20/21C. If anything the tank temperature may be a little high. Does this mean I've wasted money on a heater which I don't need? My other 30L tank definitely needs one so is this little tank in some way magic? If so would anyone like to buy a magic tank?

 

[sylvia]

Is the thermometer ok? Also, does it have lights or does it get any direct sunlight? I'm pretty shure the heater is not a waist of money - the control it gives you is invaluable - especialy if you have fish that enjoy water at a much higher temp than your room and during the night when no lights means the temp can drop drasticly - fluctuations like that are dangerous to fish as you likely know already.

 

[Slyspy]

I think the heater may be faulty. It is set to maintain a temperature of about 78F/26C and right now its little light is on, meaning that it is heating the water. Trouble is that both my external and internal thermometers give a temperature of above 82F. Which suggests a problem with the heater, though my other Visitherm is perfectly reliable. I shall look again in the morning after hours of darkness in an unheated room and see what temperature it reads then, and whether the heater is working or not.