Accurate, reliable thermometer?

I just bought another JBJ Digi-temp thermometer to replace the one that the rubber suction cup on got chewed threw over time and it's reading at pretty high temperatures. Mind you, I haven't had one in the tank for a couple weeks, so I don't know what to make of it, but my temperature never read over 82 before...usually would hover between 81 and 82. The new one said 83.7 when I put it in the tank today and hasn't dropped past 83.3 even with night fall and lights out. Is there a way to test its accuracy other than putting it in colder water or whatever?

I'm checking out some of the ones on this page with probes...can anybody recommend a top notch one to me? Doesn't have to be from that site.

http://www.techinstrument.com/acatalog/Panel___Wall_Mount_Thermometers.html

Edit: Seems like the only one on that site for aquarium use is the A150Q

I also forgot to mention my heater is set on 78. It's an aqueon 200 watt heater in a 72 gallon tank.

I have the Coralife 265 PC light hood as well...it puts out heat, but so much as to need a chiller I would say.

Something has got to be the culprit here...I just want to know the REAL temperature of the tank. Would it read higher if placed in the sump as well since the heater is in there? My thermometer is in the top right corner of the tank right now against the wall.

So if I stick any alcohol thermometer in there, that's pretty much guaranteed to be the most accurate reading and the standard to abide by and compare to?

I put the thermometer in my brand new fridge, which is set at 37 degrees. It dropped to 38.8, then I checked again later and it was at 42...unless my refrigerator is fluctuating, then there is something the matter with this thermometer.

Edit: Now it's at 47.8...umm ya. Something is wrong with it and not my fridge haha.

mike_nikki said:

A mercury thermometer is actually the best IF you can actually find one they stopped making them along time ago. but yeah, your digi is freaking out if its doing that unless the fridge is doing that by opening and closing the door alot

Click to expand...

I took it back to my LFS...they just gave me another one no questions asked. I was testing out my new one in the car on the way home and it was responding very well to the air conditioner...problem is that it was stuck onto the rear view mirror and as my friend was parking, it fell off and broke! I took the battery out and put it back in a few times and it turned on again...funny thing...I left it in his car! Will report back when I get it back and have more stats...oy.

Okay, the new one says my tank is 85.1...that's even more than the other one said! I'm going to go get one of those alcohol based ones from petsmart and see what that one says and report back.