Hi all, long time lurker, first-time poster.
Question about water thaw devices.  I'm a proponent of using the right part for the right job.  But I'm still seeing a lot of people advising others on the use of aquarium heaters.
I've been in the aquarium trade for many and I can say that using a device meant to rais room temperature water 10-15° is very different than raising sub-freezing water to a liquid state are very different items.
Aquarium heaters are fragile and have a very high failure rate, even in a stable aquarium environment.  The unfortunate thing is that they often fail in the on position which I can tell you from personal experience, can cause electrical shorts.  This is why pro and semi-pro fish keepers use a backup thermostat control that cuts power to the heater should the temperature get too high.  This is something the casual fish keeper isn't aware of and I'd suspect even fewer chicken keepers.
If the heater fails in the off position, the water can freeze and crush the capsule. This can also cause an electrical short and potentially electrocute your chickens or even cause a fire.
A quick talk with my insurance company revealed that if the fire department were called and the discovered that the fire was caused by a misused item, then they may not honor the homeowner's coverage to repair the damage.
Also, one shouldn't keep water too warm for too long as it can breed waterborne bacteria.
Lastly, (if it hasn't been mentioned before) You'd have to use a rather powerful heater to keep water from freezing. That being said, there are far more efficient and less expensive devices that are purpose made for that.