Would maybe try and observe poop from fish,to see that it looks solid as opposed to white ,stringy looking.
Might also check to seee that flesh inside the gills is red meat colored,as opposed to pink to grey looking.
This might help me to determine whether intestinal parasite or possible gill flukes might be an issue to consider given the twitching,rubbing you describe.
Have not used the medication you mention so don't know what it treat's,but Frequent water changes and re-dosing should you include meds might,eliminate, possible contaminate that may have been unknowingly introduced to the tank (deodorant/air freshners, soap or oil on hand's etc).
In less worrysome instance,and only a couple of the fish were producing excess slime coat,, then I might Consider possible fishes about to spawn where excess slime coat would provide food for fry should they appear.
Might lay off foods like blood worms,tubifex,or beef heart for a while were it me and offer quality dry pellet's if they will take them.
Could then if needed,,mix some medication with the worms ,beef heart,should intestinal parasites be evident and fish would gobble up their medicine(much more effective than treating water).
Just my two cent's.
Keep the water/filters clean!