I had a rescue with dropsy and fin rot. Treated with aquarium salt and kanaplex. Healed up just fine. Epsom salt is used for bloating and constipation. Aquarium salt can help with fungal, bacterial, etc because it creates a bad environment for the fungus or bacteria to grow in. Also helps gill function and immune system.
Epsom salt draws fluid from the body and aquarium salt causes the body to retain fluid. Dropsy is a fluid build up due to organ failure. It’s a symptom of something else going on, and often it’s bacterial. That’s why an antibiotic was suggested. Still it’s rare to overcome Dropsy, and when one manages to pull it off the fish may still have organ damage and get knocked down by another infection down the road.