heater
 

A person told me to set the heater a couple degrees below my low temp.(76) This way the heater safeguards against the temp going so low it kills livestock.

try adding an additional heater!
I use to use 1 larger heater for my reef until a freind suggested for me to use 2 smaller, I scratched my head and asked why add 2 when I can use 1?
He replied if 1 small heater stuck on your reef wouldn't cook, the likely hood of 2 failing is very unlikely and if it did I would have to go buy a lottery ticket. btw total water about 180g and am using 2 200w

If your heater is working properly, you should be able to set it at your desired temp, and it should only come on if the temp drops below that. If you set it low, you will likely have temp swings at night. I've found it hard to get a good heater that is always consitsant. Mine is working fine now, but I don't trust it. I'm thinking the answer is a good quality controller and probe element.

There's definite merit in two small over one large specially if relying on the heaters own thermostat rather than a external controller.

Didn't cook a tank but probably came close once on my old 75g when the single large heater stuck on.

heater
 

Thanks very much for the advice