A couple of years ago, we had something similar happening. In our case the tank was actually emptying on its own. Called in a plumber (we use Kiley's) and had the interior workings of the tank replaced. I cannot tell you any more than that, but the problem was solved.
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A people free to choose will always choose peace. 
Law of Logical Argument: Anything is possible if you don't know what you are talking about!
Since light travels faster than sound, some people appear bright until you hear them speak
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