Quote Originally Posted by chuck94022 View Post
I'd wager that my plastic tub was a lot cheaper (and lighter) and not nearly as deep as a fish aquarium! And the styrofoam container I used as an outer insulator was free.

In my case, the water pump was for either a large aquarium or a water fountain. The aquarium heaters have the issues discussed (and worked around) above. Personally, I think if you use a PID (which is accurate to .1 degree C) you're better off using a stronger heating element. But that's a personal preference. I have no idea how accurate the controller is in an aquarium heater, but I doubt it is as accurate as a PID controller. But it is probably good enough.
You're probably right. I've used a variation of this myself. The tub I had had a motor to keep the water circulating (avoiding hot and cold spots), and I was able to use a simple, cheap immersible fish tank heater to control the temperature. Proportional controllers are nice, but fairly expensive. Adjustment of things like fish tank heaters can be tedious, but once adjusted they stay set quite well, and I've found them to be quite adequate.