I just noticed today that my chickens' water is frozen despite being in a coop that is covered with a tarp (don't worry, I ensured there is adequate airflow) and has a heat lamp inside. I have an old, working aquarium heater laying around. It is fully submersible, but it doesn't have any way to adjust it. It maintains a constant temperature between 70-80 degrees Fahrenheit. Will that be too warm for the chickens to drink? It is bad to have them drinking warm water while it is so cold outside?