Resolved Near Disaster!!! Or was it???

So my Eheim Jager heater 75w for my 20 gallon tank has been maintaining a pretty stable temp for me around 76-78 degrees. My light heats my tank during the day at 78 degrees, then when the lights go out my heater will maintain it around 76-78. Last night I shut my lights off at around 9pm and the tempurature was normal. Then I had a late night and got back a little after 1am and looked at my digital thermometer for my tank. It was at 82 degrees and the heater was still running!!!! This scared me as I thought the heater had stuck and the tempurature would keep rising. I quickly unplugged the heater, then went to bed. 30 Minutes had past and I somehow remembered that I had a cheap back up thermometer in the back of the tank, thinking that maybe my digital heater wasn't working, so I went to my tank and looked at the back up and it read that the temp was 77?!?!?! Then I looked at the digital and it was going from 77 to 76 to 78 in the matter of minutes... I gave it a go and plugged the heater in, then fell asleep. I woke up with the temp at 77. Now I am not running my lights just to see if everything ok whether it is my heater or my thermometer. What do you guys think happend? Do you have any advice on what I should do? I am very concerned because of my live critters in the tank.

 

It's the digital thermometer, they suck! I have had 2 that have done that same thing, I will always have a glass thermometer somewhere in my tank to back-up my stupid digital ones. I doubt your heater is in question as you have a good quality heater! I used to use them when they were ebo Jaber and they were the best then! Good on ya for having a second thermometer. I would keep an eye on the temp, but I think you have answered your own question.

 

I have not had very good long term luck with digital thermometers myself.

 

good ole mercury thermometers are always going to be the most reliable

 

Aside from a controller finnex makes a great product for some piece of mind.there are other brands that make similar products if you feel like shopping but I have always liked finnex

Finnex MAX300 Heater Controller - AquaCave.com

 

It's virtually just as accurate to use any of the common alcohol thermometers they sell instead of searching for mercury. Plus who wants to have mercury in their tank if they don't have to.

 

My battery ran down and recorded 88 ! ! ! ! ! Didn't have another thermometer, so had to go with a rectal thermometer (don't ask) LoL. Long story short, the digital thermometer was discovered as the liar . New battery and she is all good.

 

Haha Rectal Thermometer......... Thanks Guys

 

use several regular thermometers

On my 75, a reef guy told me to put 2-3 thermometers in different spots. That way if one wasn't just right, the other(s) could help give a better idea of the water temp. Your tank might be a little small to need the reading in different spots, but having several thermometers could be helpful... just a thought.