Dropsy, why?

[freshwaterfishtips]

My Wantai has dropsy. I've taken care of him so well. I don't know what went wrong. So...why?

We have a 10 gallon tank, with 4 cories and 2 tetras and Wantai. The tank was cleaned every 1-2 weeks (which was recommended), our water quality's perfect. I guess it would be enough proof to say that we have two tetras that are six years old, and our danios and a white cloud died half a year ago all at the ages of five...

Our fish store was impressed.

Anyway,
We've only had Wantai since August. He's my first betta and I love him so much, he has the smartest little personality. We haven't gotten anymore fish since.

I feed Wantai 3 types of food, in good amounts:
-Hikari Bio-Gold (most of the time)
-Tetrafin Betta food (a little, for variety)
-Freeze Dried Bloodworms (Once a week, because it's good for him)

I also entertained him a lot, but not if he acted like he didn't want to be played with. I always cleaned his toys (the training ring, covered by aquarium plastic, and other little safe things) well before putting them in the tank.

Then he stopped doing his tricks and started ignoring everyone. I thought it was boredom at first, and then maybe the tetras biting him? But they weren't mean to him or anything...

And then came the pineconing, and the disaster. We have Wantai in a breeder net separated from the other fish, two of our cories are in the petstore hospital because of bacterial finrot...

The cories are healing well and are expected home on Thursday, but I don't know if I should get them yet. We are treating our tank right now with a strong, safe antibacterial

We've cared for fish successfully for almost seven years and nothing like this has happened! What did I do wrong? How can I help Wantai? Did he come with the disease, or is it something I did? *stressing out*

[LittleFish2012]

First things first, I would isolate him in a hospital tank (unless he is alone in the tank). Dropsy itself is not contagious, but what caused it might be.
Once you have him in a separate tank, start treating him. Use epsom salt to help him stop pineconing (the salts draw out the fluids from his body and therefore relieve pressure). Dissolve 2-3tsp/gal epsom salt before adding it to his tank. And for the bloating belly, keep using antibiotics. I recommend something that has a wide spectrum. If you can, keep the water warm.
As to why your fish got dropsy... well, that's always the mystery. It can be parasitic, bacterial, or viral. I don't know how your fish got it. Whatever the case, it causes some kind of organ failure (usually liver or kidneys).
Despite a low survival rate, don't give up on him! :( I'm right there with you, as I also have a fish with dropsy (not mine originally, but since he was abandonded he's mine now). For my betta, it's too late because his owner waited weeks to tell me about him. But if you just noticed his symptoms, THERE IS STILL A CHANCE!!