"From what I know of Nebraska winters, I dont think a thermostat or adjustable model will be needed. If necessary, he can use the timer running the heater."
What I was trying to say, and did so rather poorly, is that Ne. winters are cooold, and that an in tank heater wouldn't need a thermostat. I dont think you will boil your fish. They may even get some 60-70 temp water. If it got too warm, then the timer could be used. As someone alluded to, as the ground gets colder, so will the bldg. 1500 watts directly in the water beats 1500 watts from space heater. Hope I didnt confuse myself again.
