Valbazen or albendazole is a good alternative to Safeguard, to alternate. Some also rotate with levamisole (Prohibit Powder) that goes into the water. But it might be good to get your fecal float test back to see if there are worms, and what types. If tapeworms are ever a problem, I would use Equimax or Zimectrin Gold horse paste, which contain praziquantel. The ines above are not effective against tapes. Ivermectin has lost it’s efffectiveness on chicken worms according to some experts here (I am not an expert, LOL.)
I would also recommend looking for a rodent problem. Mice and rats can jump up into hanging feeders with no problem. With mice, they tend to leave droppings in the feeder, but rats don’t.