So I've had this problem for a while now... It's occurring in my female betta tank (there are generally 4 in the tank at any one time and they get along very well as they have plenty of hiding spaces and room to stay away from anyone in a grouchy mood). The tank was maybe 4 months old when the dropsy started, but fully cycled, and had other fish in it before. The first time the dropsy appeared, each fish, one by one, would start getting the symptoms, and I did lose one fish. I then treated the tank with a broad spectrum treatment (it was the best I could get my hands on at the time), and surprisingly, it seemed to work. The bloating went away, all the scales went down etc. I had healthy fish again. It was when I started this first treatment that I also changed my water change routine thinking it could have been a water quality issue. I started doing about 50% once a week instead of 25%. I stopped the treatment with the broad spectrum, and did add two more bettas, which I know isn't a smart move, but they were not getting along in the tank I originally put them in, which was supposed to allow them to grow a bit more, as they were a fair bit smaller than the ones I already had. I didn't have another tank I could transfer them to, and I thought the dropsy problem was solved, and the only thing I was really worried about was them getting along with the older, bigger fish. They actually got along fine, there wasn't even a problem with aggression at feeding time (they all come from the same place and are shipped to my local store together in one bag with no problems). While 5 wasn't my ideal number in that tank at the time, I was keeping an eye on their behaviour and was on top of all the water changes (literally putting my tanks before my health at this point, as I have been quite sick recently). A couple of weeks later (so about 2 weeks ago now) the same thing had happened again though, and again I lost one fish. Though that being said, none of the new fish got sick, only the older ones. Again I treated with the broad spectrum, and other than the one that went downhill too fast to save, the other two are mostly recovered (they are still a little bloated, and the scales are not 100% flat on one of them). I'm now scared to stop the broad spectrum though in case it comes back again ( I still have another week with it to go anyway but after that I don't know what to do). Any suggestions on how to get it to go away, and stay away would be appreciated, and also does anyone know why it's only the older fish being affected?