advice on setting temperature program

Hi,

I have an Aquatronica controller and would like to set up a temperature related program so that if the tank temperature raises too high then the system will override the timer program and switch off the halides.

I have managed to set up something similar so that if the temp goes above 25.5 then the fans kick in. However, one slight annoyance with this is that when the temperature is hovering around the 25.5 mark then for a 5-10 min period the temp reading fluctuates between 25.5 and 25.4 and the fans keep switching on and off.

Whilst this isn't a problem when it's the fan in question I would not want to set-up a similar program on my halides if there is a risk that once the temp reaches the set number then something similar happens. I would not want the halides to light up again until the temp had dropped significantly (say 0.5c or the next day).I am concerned that if something similar occurs then the halides may get switched on and off repeatedly and aside from causing stress this could blow the starters.

Has anyone set-up a similar program and how have you managed to overcome this???

Thanks,

Kevin.