Originally Posted by lilnaugrim
Yes, there is a small orange light. I position all my Hydor's (that's all I use practically) horizontally to evenly heat my small tanks. They are fully submersible and won't break in cooler water.
I still keep my heater's in for the most part and just keep them set to 78 or so for the summer time just to ensure my temp doesn't drop below 78 at least. Although, just because you set it at 78, doesn't always mean it will be at 78, this goes for almost all heater's not just Hydor. This is why having a thermometer is important, because heating a 1 gallon versus a 5.5 gallon is a big difference. The heater may overcompensate and heat more than 78 in a 1 gallon but stay steady at 78 in a 5.5, so definitely use a thermometer and adjust your heater accordingly from there.
I did emerge the heater in lukewarm water hoping it would do something but since none of the AC is installed in the house (yet) i guess maybe my sense of hot and cold was a little off.. I didnt see the heater's light turn on.. I guess i will remove it from the tank to test it in colder water or something.
I have a thermometer in the current empty tank (for the hydor heater) and it reads a little high since it is.. annoyingly warm at the moment.. my other tank (same size with 25w marina heater) i saw turn on... once.. in the middle of the night like last week when it was a bit cooler. xD so testing this heater in an empty tank totally sucks in the heat.