With salt, you need to dilute the salt in a cup of tank water. Then add it to the tank slowly. Just dumping salt can create issues. Sadly, diluting it is rarely mentioned, until there's a problem.
I don't use meds, so am unsure as to whether it will kill off your filter. Perhaps you could put the filter media into a spare container with used tank water and a few flakes of fish food to keep the bb fed while you treat your fish. Then he could stay in his known environment.
You shouldn't have ammonia readings at all. How long has this tank been up?
75: blood parrots, featherfin cat, emperor tetras, turquoise rainbowfish, BN plecos, japanese trapdoor; 46: WCMM, gold inca snails, ghost, bamboo & amano shrimp, kuhli loaches, rummynose & ember tetras, endlers, platies, flame gourami, guppies; 16: pygmy, peppered, loxozonus corys, otos, assassins, RCS ... ~ Research PRIOR to purchase.... ~