tank heaters?

[Ravo Himself]

so if any of you have read my bait tank thread i have one of those Allied Precission tractor supply 1500w stock tank de-icer in my 110 gallon tank. it got really cold and started to ice up so i plugged it in and was happy when it was thawed out a little over an hour later. being that it has a built in thermostatic shutoff i left it plugged in. my understanding is its really only supposed to keep it a little above freezing but when i checked it the next morning with an infrared gun it said 55* and i had a few dead fish. i think they got temperature shocked and died.

my question is if any of you guys have used them before have you checked to see what temperature it holds the water at? do you think this unit is just defective and running constantly? i can't find anywhere online that lists the temperature perameters on that unit but browsing the internet i found a different brand that lists 35-45*

http://www.statelinetack.com/item/farm-innovators-drain-plug-deicer/BEW11/?srccode=GPSLT&gclid=CPXanqu8jsICFYuVfgodGhoA5A&kwid=productads-plaid

maybe thats the way to go? any suggestions or input is appreciated. i would really like to get this figured out before ice season really starts in my area

[Ravo Himself]

i actually answered part of my question. found this in their FAQ section.
http://www.alliedprecision.com/faqs.html

so theirs are basically designed to run between about 40-55*.

i'm inclined to buy that other de icer being that it supposedly runs 35-45. is a 10* temperature change going to shock the fish? granted its not instant but i don't want to stress the fish out. am i better off buying one of those smaller aquarium heaters and just let it run all the time and use the deicer as a backup thaw method, or go for the tried and true heat lamp method?
i just really like the idea of the deicers because you can leave them plugged in and they will regulate it for you