I cleaned out my turtles tank yesterday and found that one of my turtles has a smaller dark soft spot on the bottom of his shell that looks like its rotting from the inside. Its very soft if I put very little pressure on it moves and any more it would rip open. I don't have any money for vets just got laid off and wont get unemployment for 6 weeks or longer. Does anyone have any suggestions on what it would be and how to treat it? Here is a pic too. Thanks for looking.