i tihnk my beta is sick but i am not sure

Question
I have had my Betta for about 5 months now. I bought him from Wal-mart, and his name is Kamieko. I used to keep him in a one gallon vase but after doing some research decided to upgrade to a 10 gallon tank with stones on the bottom and two different fake plants. he's been in the tank for about 3 1/2 months now, i feed him tetra freeze dried blood worms, aqua culture betta food, and san fransico bay brand freeze dried brine shrimp. I usually only feed him once a day, i give him 3 pellets and then 3-5 worms or shrimp (i alternate the worms and shrimp) depending on how quickly he eats. i always make sure he eats all of his food and do not let any float. I do 100% water changes once a month and 1/3 changes twice a month and i use water conditioner, bottled spring water, and a filter, and i keep his temp between 76-78. he usually seems very happy and not stressed out, he always ate really well, up until about one week ago.

lately he cannot eat. he tries very hard to eat, but it seems like he cannot suck anything into his mouth. he stays close to the top and in corners, and his fins are not clamped, he lets them dangle below him. he's not swimming around like he used to. i cannot see any white patches on him and his fins are long and colorful. the ONLY problem is his eating and inactivity, why can't he eat the same things he has been eating for months anymore? it's so pitiful to watch and i am so scared he is going to die from starvation. he bites at it and sometimes jumps out of the water a bit trying so hard to get it into his mouth. i cannot see any flim or anytihng on his mouth and it is opening and closing correctly, but nothing goes in. he gets frustrated and gives up very quickly and retreats to a corner. his swimming has become a little more erratic, either that or he is weak from not eating so the filter is pushing him around easier. what do i do? what's wrong with him? i haven't read anything like this yet.

I am thinking about putting him into his smaller tank and buying some fungus eliminator by jungle and some aquarium salt by alpi and treating him in the vase for a little while and doing water changes very often during this period. is that the right thing to do? what am i missing?

PLEASE HELP! thanks.

Answer
Betta fish can live up to a month without food, this is a extreme measure though. Make sure there is good circulation in your tank and enough oxygen. However, you don't want circulation where your fish doesn't have even control to swim on himself. Make sure your filter is suitable for your tank. If you don't already have one, go buy an air pump to run into your tank. When fish are deprived of oxygen they tend to hangout at the surface of the tank. Complete a water change to ensure your water is nice and clean. Is his belly swollen? Is he passing fecal matter? He might be constipated. Often, when fish are constipated they loose their appetite. I wouldn't treat him with fungus medication unless you see symptoms of it, such as white cotton like patches. Try not to stress him out too much, meaning keep him in the same tank. Any other question feel free to ask. Hope all works well.