My current method of fermentation temperature management is submerging my carboy into a large bucket of water. I regulate the temperature of my water with ice packs/frozen water bottles to keep it at the desired temperature. I use a pretty large volume of water so temperature fluctuations are minimal, maybe a degree or two over 24 hours.
My concern is that I am setting the temperature of the water to the desired fermentation temperature but the actual temperature inside the carboy is somewhat higher.
My question(s) are,
First, what is the best way to get an accurate temperature of a fermenting wort? I have read some responses to the question How many degrees will my carboy heat up as a result of fermentation activity? and after further research am uncertain that a stick on thermometer will do the job since it is positioned on the glass and likely to be affected by outside temperatures.
Second, is there a way to calculate the appropriate temperature to set the environment, in my case bucket of water but could also be a fridge, to in order to appropriately compensate for the added heat of fermentation?