[George]

I keep hearing people suggesting multiple, small heaters in a tank to minimize the impact of heater malfunction. Well, it may slow down your temperature going up in the event of one or more heaters malfunction. BUT, with three heaters in your tank running parallel, now you have three times the chance of getting a malfunction heater.

It may be a better idea to hook your heater to a temperature controller. If the tank temperature hitting a set point, you can instruct the controller to shut down the heater. Then again, I haven't seen a stand-alone heater controller for water. Most aqua controllers are expensive due to all-in-one design.
If someone can design a heater controller, I don't think it will cost more than two heaters. Or can it? hint, hint...

I don't know. I am just throwing ideas for discussion here.

Thanks for your time.
George