10-02-2011, 01:15 PM
| || |
Some tweaking required.
As 1077 pointed out, you can do this right in the aquarium. Start with just one heater and get it set and stable for the correct temperature (the other heater can be in the tank, but either unplugged or set low to not interfere.
Once the temperature is stable with just the one heater, turn on the other heater and adjust the temperature control so the heater just comes on. Monitor and adjust as required. Don't be surprised if one of the two heaters is slightly more dominant than the other - eventually, they will be very close.