It may not be from poor water conditions, but that is just the number one cause. What i have learned though, is that your water parameters can be excellent, and you could be doing water changes, but there could still be something polluting the water, some kind of decaying material.
Some ways to check your water, smell -your fish water should not have a bad odor to it (though carbon filters usually hide any odor), look- put some water in a plastic cup, it should look clear like water from your faucet, surface agitation - if you agitate the water, like by swishing your hand in it, the bubbles created should dissipate really fast. If you do find you have any of those problems it would probably be best to do like a 20% water change daily until it clears up.
But if it is bacterial you need some medicine that will work on internal infections, that is probably your best bet if it is dropsy.
I know your tank is relatively new, you water may be perfectly fine and I notice I have been ragging on you a lot about poor water quality, I just want you to know I am not trying to insinuate anything or say anything bad about your water, it is just fin rot and dropsy are usually symptoms of poor water conditions.