Yesterday, I got a new 20 gallon Top Fin aquarium. It came with a heater a filter and a thermometer. The thermometer is one of the digitial ones (which I have found I don't like) and I was wondering if it goes on the outside of the tank or the inside. I originally had it on the outside, but then moved it to the inside. If it is meant for the outside will it make the water toxic with it being on the inside?
