DO NOT PUT A STICK ON THERMOMETER STRIP ON YOUR CARBOY!!!
The water will seperate the temp strip from the plastic cover and it will be ruined permanently if immersed.
Use a dial thermometer in the water.
To save $$$ on therm strips use them only when your carboy/bucket will not be added to a tub of water. How? Easy...
First off, do not pull the backing paper off of the strip. Place 3" wide packaging tape over the strip and fold the top edge over about 1". Whenever you want to place a fermenter in a tub of water you can remove the taps and strip and reuse it on another fermenter. When the tape goes bad just cut it off and add another piece of tape.