Unfortunately you can't treat dropsy unless you know what is causing it. Dropsy is tricky =/.
Feeding some pieces of a boiled and skinned pea often helps.
And if it's just because he ate too much then only feeding the pea and nothing else will help him get back to normal.
If you think he is overweight then just reduce the amount you are feeding him and try to get him a bit more active. Of course you can't take him on a walk or anything (lol) but even just scattering his food so he has to swim around and look for it will help.
What worries me is the fact that he is starting to "pinecone" (the scales being raised). That's never a good sign. A good idea would be to give him a salt bath with epsom salts. Basically, you put him in the salted water for about 10 minutes (a regular 1-gallon container is fine). You may end up having to do it again the next day. Use a tablespoon of epsom salts per gallon. If you do it a second time you can increase the amount of time he spends in the bath.
The epsom salts should really help especially if this has to do with bacteria.
You definately need to seperate him. Because if this was caused by an infection then the other fish could catch it.
Sadly, dropsy is probably the hardest thing to completely treat
. But the salt baths and peas will at least make him feel better. And sometimes fish are able to survive...I've known of a few personally
So, in short this is what I would recommend: fast him for a few days except for the occasional piece of a pea, give him an epsom salt bath, seperate him from other fish, and vacuum the substrate daily to keep things clean.