Hot water tank, water gets cold quick, double t-stat

My hot water tank hot water doesnt last as long as it use to. I drained the tank down to see if anything was sitting on the bottom of it, and everything seems ok. A little bit of stuff came out of it that looked like sand, it wasnt very much at all. After it was drained I shook the water tank a it felt empty, and also light. I noticed that it has two thermostats on it, is it possible that one of the elements went bad and one heater cant keep up. If that was the case though I am guessing that the water temp would suffer as well. Not the case as the water is hot just like always, just the length of time the water stays hot has suffered. The water tank is about 10 years old. Any ideas?


Most likely the bottom element is not heating. Or the dip tube could have failed.