my first betta boy Bart has Dropsy!

Hes all fat and looks like a pine cone! he was a little puffy yesterday, but when i got home tonite he looks terrible. i feel horrible for him. ive treated him with Maracyn-Two but is there anything else i can do for him? hes still eating now but i dont know how long that will last. im afraid im going to loose him because everything ive read says its almost always lethal. has anyone had one come through ok?
Housing
What size is your tank? 3 gallon
What temperature is your tank? 78 degrees
Does your tank have a filter? yes
Does your tank have an air stone or other type of aeration? no
Is your tank heated? yes
What tank mates does your betta fish live with? none but does have live plants
Food
What type of food do you feed your betta fish? tetra bettamin tropical crisps
How often do you feed your betta fish? 1x a day
Maintenance
How often do you perform a water change? every 2 weeks
What percentage of the water do you change when you perform a water change? 50% every 2 weeks, 100% after 2 50% changes if that makes sense.
What type of additives do you add to the water when you perform a water change? aqua safe
Water Parameters:
Have you tested your water? If so, what are the following parameters?
Ammonia: 0
Nitrite: 0
Nitrate: 10
pH: 7
Hardness:
Alkalinity:
Symptoms and Treatment
How has your betta fish's appearance changed? Fat & Looks like a pine cone
How has your betta fish's behavior changed? hasnt changed much, still eating
When did you start noticing the symptoms? he looked a little puffy yesterday, looked swolen and scales poking out like a pine cone
Have you started treating your fish? If so, how? 1 packet of maracyn-two
Does your fish have any history of being ill? none
How old is your fish (approximately)? 2 years