New Heater -- can't tell if it's working

[agent89201]

I just got a heater for my fish. It's a small one for a 2.5 gallon tank and is preset to 78 degrees. I figured since it was pre-set, I wouldn't need a thermometer so I didn't get one. But I can't tell if it's working or not. The water seems cool one minute and a little warmer the next. I'm thinking I should have bought that thermometer.

Should I turn it off and take it out? Should I leave it in? Advice please!

[Kytkattin]

Unplug it tonight (but leave it in the tank) and go buy a thermometer when you get a chance. They are pretty cheap, especially compared to all the other things a tank needs.

[EvilVOG]

having a thermometer or other way to monitor the temp is a good idea.

the problem with those pre-set heaters is that they only raise the temp about 4 deg. above room temp (or whatever it thinks room temp is) I own one and have watched it range from 74 to 86! It was perfect when i kept the tank in a more stable location (temp. wise), but where i have it now closer to lights it was overheating the water during the day, and not keeping it warm enough at night.

So when you get a thermometer you can watch it closely to know what it's doing better. That will help you decide if it suits your needs properly or not. Or you could just return it for an adjustable 25w or so. The people around here advise higher wattage that what the packages say they're for. So you would want one that says it's for a 10 gallon.