Hello everyone! Last spring someone gave me a tank he needed to get rid of. It holds 185L/48 gal. Due to its size and lack of space I keep it outdoors on an oversized window-sill with no heating or anything else that runs on electricity: there is no way to connect to electrical power. It was an ideal summer residence to 1 harlequin, 2 pygmy cories, and 3Everglades pygmy sunfish. The winter of 2016-2017 was the coldest one in some 40 years. Generally temperatures rarely go below the freezing point here but this time entire towns in the area remained without water in February due to the frost, water pipes exploded. My question(s): - Has anyone experience with unheated outdoor tanks? - How many days, if any at all, can the surface of the water freeze without damaging the tank? - Is adding salt an idea? I have vague high school memories of the lowering of the freezing point when something (salt?) is added to water. It would be disastrous if the glass cracked. Due to its size and weight the tank is already difficult to handle when it is whole, I don't want to think of how things would be if it was damaged. It would be difficult to dispose of. The coldest it got lately (at night) was about 4C/39F. But with some luck it will not get much colder than that for a few months to come. The water temperature is 7-8C/44-46F. Many thanks in advance for any answer!