The thickened slime coat can be caused by anything that irritates the skin, that can be costia, several other parasites, or water quality issues, like high ammonia, which burns or swinging pH going from alkaline to acid, due to low KH. So before treating for parasites, be sure to verify that there is not an issue with high ammonia, or major changes in pH morning to evening. For the one with dropsy, once you have caught it, if it has a large ulcer, the salt at anywhere from 0.6 to 0.8% will help to relieve pressure on the kidneys by reducing the osmotic pressure from low salinity to high salinity where the fishes blood has a salinity of 0.9%. At the higher salinity, then antibiotics will help the ulcer heal by treating the bacterial infection causing the ulcer. The antibiotic can be injectible Baytril if your vet will work with you to supply it, but if not, then Tricide Neo is a good alternative, and further down the list is Triple Antibiotic Ointment. If there is not a major ulcer causing the dropsy, I don't think the salt will do much. Dropsy is a symptom of the kidneys not being able to expel enough water from the fish to keep it from bloating up, and that can be from too much water entering the fish, as in the case with an ulcer, or due to kidney failure. If kidney failure, the use of antibiotics are not very effective either as they are hard on the kidneys which are already compromised.
Zone 7 A/B
Keep your words sweet. You never know when you may have to eat them.
Richard