Hi & welcome!! What size tank is the shubunkin in? What are the exact water parameters (ammonia, nitrite, nitrate, ph)? Dropsy is a symptom of disease & not a disease itself. It can be caused by various things such as poor water quality, an internal bacterial infection, parasites, or a virus. Is the fish in question pineconed (bloated, scales sticking out)? I believe Scotland follows various other European countries which strictly limit fish meds to veterinary use only. You will need to seek out the aid of an aquatic vet if you want to try & help him. Good luck!