being that i have very large teethed playful fish, putting anything in the tank that does not get broke or eaten is a real challenge. sponge filters get picked apart, thermometers get rolled around the tank like a ball.... you think of it, they play with it. some of the newer filters have thermometers in them, along with heaters which mine are also playing with. at night you can hear it tapping against the glass. use a stick on type outside of the tank and when i do my feedings i hold the thermometer in the tank for five minutes to get an accurate reading. you need atleast 3-5 minutes of being exposed to the water to get an accurate reading.
semper fi