He might be just tired of the same kind of hay. Mixing the alfalfa with some other kind might help.
Dry poop is usually a sign of lack of water. Does he have salt available?
I would give him more beetpulp, soaked of course, to get some extra water in him. Add a teaspoon of salt to his feed.
Have his teeth been checked?
Dewormer: best would be to do a fecal test and deworm him for what he actually has. Then a dose of Equimax/ Zimecterin Gold, to catch eventual tapeworm.
ETA- normally for every two lbs of hay you can take away one lb of senior feed, if you feed the recommended amount without hay( does that make sense lol).