Ive never had this...this is cut from this link
http/www.fishforums.net/index.php?/topic/59440-a-to-z-of-tropical-fish-diseases/
If you have the possibility of a "Hospital tank" id highly reccomend this course of action
"Dropsy
*Problem occured with male guppy*
There is no cure to this disease, but I have heard that improving or correcting the tank conditions and diet may help.
The cause of dropsy is either oragn failure or enviromental factors: excessivesodium chloride levels, high nitrite levels, bacteria, orpoor/unsuitable diet.
*Conclusion with my fish: Still has Dropsy... things not looking too good but still trying*