If you had a heater in the tank the temp would never drop below the set point even on cool cloudy days and you could still do what Myka suggests if you want to.

I do have a heater in the sump (200W) but every single heater I have, about 10 different one's, will not stay at a steady temp. For some reason they all seem to creep up and have to be adjusted daily. If I had a controller it would be a hands free way to maintain temp.

I'm using a type of logger to control a couple of muffin fans over my sump and a heater. Found temperature stays within about a degree throughout the day. The logger controls the tank temp but have the heater's internal thermostat set a little higher than where I want the tank as a backup (for shutting off).

Would you guys like this moved to the equipment forum for discussion ?
Thanks

What about this one from BRS
http://www.bulkreefsupply.com/store/...ontroller.html

That one would be great if there was a 2 stage model or might have to get two.

Keep an eye on Reefcentral and you'll find great deals on Rancon dual stage controllers. I bought one and would never be without one again. They are aupposed to be the most reliable controllers.

This is what i did with my controller, i bought this: http://oceanaquatics.com/store/produ...er-Controller/ then hook up a 120v relay, then hook up the fan to normally close on relay.
The operation will be:
1. Temp controller on= heater on= relay energize, fan off
2. After reaching desired temperature= temp controller off= heater off = relay de-energized = fan on since it is connected in normally close..Basically the fan will only turn on when the heaters are off..
This is the cheapest for me and it works.

tedy