I would not worry about it too much 27 C is 80 F many reefers including myself will run their tanks at this temp. I would say if you start hitting 32 C it is time to take so action. What you do not want to do raise and drop temp's too quickly. You would be better of just leaving it. Something I was told a while ago by a friend in HAC is to run Thermostats in Imp. or standard mode as the equipment is more controllable in Fahrenheit.
Example 1 degree C is 1.8 F so instead of dealing with a 1 degree shift you are dealing with almost a 2 degree. I must say that when I switch my house Thermostat to Imp. I noticed a much less swing in the feel of temperature in the house, does not sound like much but at almost 2 degree swing and add Humidity it is, and I noticed the Furnace and AC works much better, as in it has an easier time holding it at the set temp. So if you have temp. controllers you may want to set them for Fahrenheit.
