Help, My Betta Is Starting To Pinecone, Is It My Tank?

[sourpatchbaby]

Backstory, we had a betta that came to us with Swim Bladder and was bloated. He was very active and although the Swim Bladder fixed itself, the bloating got worse and he pineconed and died about six weeks later. After he died I sanitzed the tank, plants, gravel, and decorations using a bleach solution (I boiled the gravel though). I put a few Molly fry in there and we got a new betta which we've had for about four weeks now. About a week ago he started getting bloated so I fasted him and did the API General Cure treatment on him just to be on the safe side. Yesterday he was more bloated even though he hasn't eaten in a few days and I just noticed a definite start to pineconing on his scales. Could it be my tank that has something wrong with it that's making the bettas sick? Is there anything that can be done to save him? He's in a heated and cycled 10 gallon. Should I redo the API General cure or get something else? My store only carries the API general cure and not the Erythromycin or Maracyn.

 

[Wildbetta]

Can you get pics of your fish?  Preferably from the side and from looking down over top of them.    What is your water temperature and do you have a heater?  What are you feeding?  Also what are your tank parameters? (ammonia, nitrIte, nitrAte)

 

[sourpatchbaby]

The tank is heated. The temperature earlier was set to 26C (so 78.8F?) and I put it to go up to 28C. It's not there yet. He gets Omega flakes as his highness doesn't like pellets. GH is 120, KH is 80, PH is 7.5, NO2 is 3, NO3 is 40. I ran out of ammonia tests so I don't know what that is but I did a 25% water change earlier today. Let me figure out how to post pics
This is him from above


This is him from the side. He was completely fine until thursday when he started to bloat


This is a closeup of his tail. The little dark dots in his fins were not there before last week. Not sure what they are as his fins don't look like they're eaten up or ripped

 

[Wildbetta]

It sounds like your tank is not cycled if you have any nitrIte reading.  NitrIte is very hard on the fish and may be one of the main causes of your issues.  Most likely have ammonia readings that are not safe either.   I suggest you start changing at least 50% of your water every day and monitor the NO2 reading -- trying to get that down to 0 as much as possible.  I also recommend you get yourself an ammonia test too.  Are you using test strips or a liquid test?  
 
As far as feeding, flakes are not recommended since they are bad to cause bloating and constipation as well as foul the tank water since the amount is extremely hard to monitor.  I recommend working with your betta to get them on pellets.   
 
At this point, you need to fast your betta for no less than 3 days to see if he starts to lessen the swelling. You can also do epsom salt baths to try to lessen the swelling.  1 tablespoon per gallon of water for 15 to 30 minutes depending on how the fish acts.  Your poor boy appears to be suffering from dropsy which is a symptom of a lot of different things.  Basically your bettas kidneys are failing and he is retaining fluid.  Prognosis is poor at this point, but I have seen fish rebound that were worse than this so there is hope.