Two heaters?

  • We are currently upgrading MFK. thanks! -neo
try putting them in a smaller tank, like 20 gallons or so, one at a time

calibrate each one to the temp you want and they should be fine for the larger tank afterwards!

I wouldn't do that with fish in the tank though as a 300 watt heater will heat it up way too fast and could harm the fish.
 
Assuming you have more than one tank, if one of your tanks is the temp you want, it's easy.

Unplug the heaters and let them sit in the tank with the right temp for about 1/2 hour. Plug one of the heaters in and turn the knob until the "pilot light" comes on. Back it up until the light goes off. Now do the same thing with the other heater. Unplug the heaters and put them back in your preferred tank. Plug 'em up.
 
What type of heaters do you have? It you have one's with internal thermostats, It shouldn't matter how many you have.
 
MonsterFishKeepers.com