For those asking, the guitar is a Yamaha FG345, my father got it in his teens and he's in his sixties now. Honestly can't tell you guys what gauge the strings are, I haven't changed them in years (I love the sound of dead strings, and these ones in particular just feel right). The strings detune when I'm not using the guitar and only during the summer. I leave the guitar in a stand when not in use. Would it be better to leave it in my black soft case and leaning against the wall, in the coolest room I can find?
The strings are not detuning A LOT between every session, just on especially hot days it's noticable that the heat has taken it's toll on the strings.