Beta fish sick

Question
I have had betas for 12 years. I bought Buddy 6 months ago. He lives in a 1 gallon vase with live plants on top of my fridge. I only fill it 2/3 full of 3 day sitting tap water. I have only fed freeze dried bloodworms. He is falling to the bottom of the tank and losing color on his fins. He eats well but falls back down on the plants. He is not bent or bloated, no bulging eyes. Has had no contact with any fish.
I do not use any water conditioner or sea salt. I never had to with the others. My apt temp is at 72. always been that temperature. Kitchen light on all day. Please help my Buddy. I have been to three pet stores and all have different answers.

Answer
Is he able to get to the surface(don't know where, exactly the plants are)?  He needs to be able to breath at the surface.

72 is a little bit too cold for him... It may be that Buddy is just sensitive to cooler temperatures, and this is bothering him.  An easy way to help figure this out is to use a lamp, generally a goose neck hallogen lamp is the best.  This will heat the tank and you will be able to determine if he's suffering from the cold.

Now, even though he's not bloating, bloodworms aren't a good staple food.  I myself prefer a commercial flake, but am currently trying a sample of Hikari gold that I was given.  Some betta pellets are too large for their mouths, and they become unable to properly eat and digest these pellets, while freeze dried foods are low in nutrients and can absorb water in the fish's gullet, causing bloat and constipation.  Freeze dried foods that have been soaked for about 10 minutes in water from the aquarium can be given as a treat, but again do not have the nutrients to be used as a staple.

Now, does your fish struggle to swim up from the gravel?  does he seem to sink and have difficulty moving from the bottom?  If so, he has a problem with his swim bladder.  Unfortunately some cases of this are chronic and will reccur regularly.  To treat him if he's having difficulties rising from the gravel, I would add about a quarter of a teaspoon to his water when doing the next water change.  This may help.

Definately find a different food, and use a lamp to warm the water... I'm sure I don't have to remind you that just adding warm water to the tank can and will cause the fish to go into shock!  Hopefully this helps out, but if not, feel free to send me a follow-up and I'll be sure to help you more.