Swollen discolored Betta King Fish

Question
Hi,

We got a beautiful blue Betta King about 8 months ago and the past month or so I've noticed that he looks swollen and seems to be having trouble keeping balance.  He mostly tries to get himself into the top of one plastic tree in the tank (came with the set) so that his mouth is just at water line.  Then he just lies there on his side not moving at all.  If I pick up the tank lightly (worried that he may be dead) he will move, but struggles very hard to get up when he falls to the bottom.  I'm crying about him and know I'll have to tell my daughter that her fish is probably dying...Please, if there is any way to save him, please let me know what I can do.  I change his water whenever it gets murky; maybe every 2-4 weeks depending... I use filtered water and let it sit overnight next to the tank to get the right temperature, then add decholrinization drops and mix before putting him in it.  I've even tried something I picked up called API Bettafix which is a natural medication for Bettas (daily drops in water).  We love this fish (Snoopy).  He's the only one in the tank; it's about 1.5 quarts and is kept on her bookshelf in her bedroom (shaded sun through windows).  We keep the house at about 73 degrees in summer and 66 in winter.  At the beginning we were feeding him every day a few Omega One Bettta flakes and then were told to feed him every other day just one or two flakes.  We also tried feeding him TopFin Betta Bits which he seemed to like, so then we sort of rotated for a number of months.  Now I don't see him eating at all...he barely moves unless he feels threatened (only me check that he is still alive).  Thank you for any help and for your time.  It's mean's so much to us.
Sincerely, Laurie (and Cadhla) O'Sullivan

Answer
There's a lot of things you can do to fix this situation, and a lot of things that you aren't doing that you should be that will make your betta much healthier and give him a chance to live much longer.
First of all, waiting until his water "looks" dirty is not acceptable. All fish release ammonia as they breathe and poop, and ammonia is toxic to them. If the water with this toxic substance is not removed regularly and replaced with fresh, clean, dechlorinated water, then your fish will begin to suffer and become very sick, and eventually die. Ammonia, by the way, is invisible. So "looking" dirty is not how you tell whether a fish's water needs to be cleaned.
Secondly, cleaning out your fish tank - no matter how large or small, should never be done less than once a week. And the smaller the tank is, the more often you have to clean it. In that regard, it is actually MUCH easier - especially for beginner fish keeper's to use larger tanks. The bigger, the better. Mostly because it takes so much longer to fill with ammonia, but for a variety of other reasons as well - such as larger bodies of water hold warm temperature for a much longer time.
Third, right now your fish is suffering from SBD (Swim Bladder Disease) and poor water quality. Change out his water straight away, and keep doing it once or twice a week. You can not slack off on water changes, it is a vital part of keeping your fish healthy. (The larger the tank is, the less water you take out, in case you're wondering. For example, in a five gallon tank, I would recommend only changing out about 2 gallons of it every week, instead of the whole thing. If you want to learn more about why this is a much better way to keep your tank and fish healthy, do some research on the Nitrogen Cycle).
To help with the SBD, stop feeding him for two days. Then, from now on, only feed him betta pellets. It's much easier to prevent overfeeding with pellets than with flakes, a common mistake made by even experienced fish keepers. Overfeeding cause the gut to push against the swim bladder, causing pain in the fish and making it nearly impossible for it to float right, in severe cases causing death.
Feeds no more than 2-3 pellets each day, and if you can separate the feeding throughout the day, instead of doing one large feeding. Fish are grazers by nature.
Last thing, you need to buy a small heater for your betta tank. They are tropical fish, and it is not acceptable to keep them in water less than 78 degrees F. You'll have to gradually get him used to warmer water of course, otherwise you'll shock his system. But once you get him closer to the right temperature, keep it steady somewhere between  78-85 degrees F at all times.
I hope this has helped you in better understanding your betta's needs. If you need more information, there is always plenty online, as well as in books from the pet store, and from the actual associates themselves. It's a really good idea to learn as much as you can about a new pet before bringing it home.
p.s. Are you using tap water conditioner? If not - start right away! Chlorine burns a fish's gills.