Betta Belly Bloated

Question
Background: I got Gandalf about 6 weeks ago, he's in 6.6 gallon tank, 24" long x 8" deep x 9" high. Filter with lowest flow setting. 3 live plants, no other fish, large hollow log for him to hide in or swim through (bought at fish store, sanded down smooth and made sure no sharp edges, made of resin or something, not a real "wooden" log). Carbi Sea Instant Aquariam black "sand gravel" very soft. No heater as I am in S. Fl and the thermometer always reads 78, however I have no problem buying a heater if it is recommended. Used water conditioner that said "instantly makes water safe for bettas" when set up tank and when I do 15% water change weekly. Test water every 2-3 days, ammonia, nitrite and nitrate have always shown zero. PH registers at 7.4.

Food, I started out feeding 2 pellets in the am and 1 at night. About 3 wks ago his belly got really bloated and he was "bobbing" on the top, couldn't seem to get down to bottom of tank, sometimes on his side, would wedge himself behind filter so I turned it off for a few hours. I stopped feeding him and read everything I could find online. Did the pea thing, blanched, peeled, small pieces.. next morning was fine. Let him fast that day, then feed one pellet softened 10 mins in some of his aquarium water, 12 hours later all bloated again. Fasted another 24 hrs, better, feed one freeze dried bloodworm, 12 hrs later, bloated, fasted and did pea again...I assume from everything I've read this is swim bladder issue and not dropsy because it does go away with the pea and or fasting but not for 24 hours or so. I've read so much in the last 3 weeks I'm so confused. Most websites say it's good to give pea, one said peas would "permanently damage his digestive track" so I'm hesitant to continue with it. Some say put salt in tank for better health, help with stress, etc. Another website said you cannot put salt in aquarium if you have live plants. Some same medicate, some say don't. Alot are recommending Daphina, what is that and where do I get it? Should I switch to flakes? Are they more digestible? I don't know what to do at this point, I can't accept that he will have to live his life on one pellet every other day and be bobbing around unable to swim on the alternate days, there's got to be something I can do. Please help, thanks so much

Answer
Lori,
Sorry to hear that you Betta is having problems. With the live plants in the tank, I would not recommend adding salt to his water. The temperature, that the Betta tends to do much better, is between 80 and 82 degrees. Even though you live in Florida, the temperature is going to drop at night. With a heater, it helps ensure that the water temperature stays consistent. Constant temperature fluctuations can cause the fish to stress, which brings on illness. With a heater, if the water temperature drops below 80 degrees, the heater will kick on. It will not turn on unless the temperature drops, so you don't have to worry about him being too warm. Do you see him going to the bottom "searching" for food? He could be digesting sand. Even the Betta looks for food and like to "clean" the gravel. I would watch him for that. If he is "eating" the sand, I would think about removing it and putting in gravel. I have never had problems with the gravel being too sharp and tearing a tail or fin. Normally, you want no ammonia or nitrites, but nitrates are helpful for your fish. It is odd that your nitrates are registering at zero. Make sure your liquid water tester has not expired, and if you are using test strips, I would toss them. The strips are not accurate. If you are having your water tested at a pet store, make sure they are using a liquid testing kit and not the test strips. As for the bloating, have you given him an Epson salts dip? This salt helps draw out the excess fluid. When you give a bath or a dip, you make the salt water in another container, remove the Betta from his tank into the container with the salt. You then let him swim in it for 10 minutes and no more than half an hour at a time. If you do this, you have to be able to keep an eye on him in case he starts having problems and has to be removed. You make fresh salt water every time, never using the same water twice. You can do this once or twice a day for a couple days and see if this helps him. The ratio is 1 teaspoon of dissolved Epson salts to 1 gallon of water making sure the salt water is the same temperature as the water in his tank.
Betta pellet food is better for him than flakes. I do not know what you feed him, but I use Atison's Betta food. I cannot get it at a store, I have to order it online. The Betta's stomach is the size of his eye, so over feeding is very easy. The pea will not harm him at all. I fast mine one day a week and feed them all a cooked shelled pea the next day. I have been doing this for over 30 years, and have never had a problem.
As for the filter, Betta's do not like them nor do they need them. The male is a very slow swimmer and when you add a filter, they have to work harder. This will also cause stress that leads to illness. Since he has a Labyrinth organ, he goes to the surface of the water to breathe. Since you are doing weekly water changes, the filter really is not needed. The only tanks I own with filter, are my fry tanks. None of my 30 adult Betta's have filters in their aquariums.
I would try the Epson salts bath and see if that helps him. If it does not help, he might just have a health problem that we will not be able to cure. Let me know how he is doing after you give him a bath.