My 900 gallon cistern for my graduate project has frozen into a 900 gallon ice cube! I can't open the release valve, its frozen solid. Not that anything would flow out said valve at this point. I guess there will be no more experimentation until there is a SERIOUS thaw. That is, unless something cracks due to the expansion of the ice... In which case there may not be any more experimentation at all. Fabulous.