Betta Won't Eat, Floats, but then sinks without food.

Hey everyone!
i just got two bettas yesterday from petsmart, a red one and a blue one. the blue one, pinky, is having a bit of an issue.
he wont eat at all, and he does this weird floating thing where he floats to the top but instead of his mouth reaching the surface, his back where his fin is reaches it. he just sits there and doesnt move.
both fish are in the same tank (its a divided tank) and there is a little plastic tree and rocks on the bottom.
i put him in reverse osmosis water so there would be no chlorine, and tried to give him flakes. he would look at them and just sink to the bottom and almost sulk.
he still has a horizontal stripe, so i'm not sure if he is just being stubborn and that is a part of his color scheme, or if he has an issue and needs to be taken care of.
the other fish, the brain, is doing fine. he eats when there is food, and is very energetic.
i washed the tank and everything in it (there is no filter or anything, the water gets changed once a week, 25%), and i have made sure that their divider is in place completely.
his fins and everything are healthy looking, no fungus or bacteria that i can see. he was a lively fish in the cup from petsmart. he also meets requirements for having two eyes (one of my boyfriend's bettas does not have two eyes, he was born with only one. his name is one-eyed jack.)
overall, pinky looks healthy, but is not quite right. i just dont know what's wrong.
thanks

How big is your aquarium? If it is those 2.5 gallon tanks, you are overstocked and that puts stress on the fish. Although I am no expert of Bettas, I know they breath air. Although they can breathe air, they still need to be able to use their gills to regulate themselves so you should at least provide them with a filter. Also, using reverse osmosis water leaves the water pristine but leaves the water unstable and causes ph fluctuations unless you add chemical buffers. I think one type of buffer is magnesium chloride. Hope all goes well.

its a tiny tank, i got it from walmart. they dont have a lot of room, but i dont have much of an option for places to put them. i have a cat. she loves fish.
i took him out of the tank though and put him in a glass jar not much bigger than his half the tank with some tap water that i treated, so i will see what that does.
i also have a guarantee thing from petsmart since i got them two days ago, so i am going to see if they have any suggestions for medicine if he is sick or if he is just in shock.
this tank is tiny, they dont have that far to get to the top. there are two fish in the same tank with a divider and one is doing fine, so i think he is just sick.

i know what bowl/tank thing you have its SMALL and even to small for one. i have one and i took the divider out and use it to put in a tank for breeding.the one you have thats sick has a swim bladder problem and most store bought bettas have this from being in a small cup for a long time and not getting changed. if your walmart is anything like mine they get the bettas in throw them in a cup shove them under a light and let the sit there in the back of the store so no one buys them untill they are all sick. everytime i see the bettas in walmart the cups are half empty so green with alge you cant see them and half are dead or have serious problems.

for a betta to be healthy in that small of a bowl thing they NEED to have the water changed 100% each day and they even make it easy and put a drainer on the bottom of the bowl thing. i would expect your one sick betta to not live long and if you want your other betta to live longer i would get it AT LEAST a 2.5 gallon tank or BIGGER.

and as i was typing all this i saw your name i play play flute to and love bettas

If the Betta has swimbladder disease as animefan says, you can easily cure it. Just get frozen peas that you get at your supermarket and thaw one or two. Once they are thawed, feed them to the betta. During this period do not feed him anything else.

my betta does that sometimes to tell me he doesnt like the water temp. no i dont speak fish but i kno if it is to low or to high they will not eat at all. also i have a female from petsmart, to be honest they are not the healthiest fish around. i have to female bettas both the same age and the 1 from petsmart is half the size of the 1 i got from big als aquarium place. and they are only about 2 months apart in age. so try the water temp thing and see if that works

One of those baseball size Betta bowls is almost impossible to keep clean, and the result is almost always a sick fish.

everyone i've spoken to at every pet store has told me those tanks are fine for the fish. i put bamboo in it, so hopefully it will help with the grossness that will probably take over the tank in time.
i dont think a swimbladder problem would make a fish not even realise there is food in the tank. he doesnt even acknowledge it now. he just floats.
i will try the peas, but i am pretty close to taking him back to the store and letting them take care of him. i'm not made of money, i'm a college student! =]
i also dont have a lot of space. i have a cat, so it doesnt work out for me to have a huge tank she can get into.

most petstore people dont care about the fish and dont really know much about them though. the swim bladder problem could be strssing him out and that makes them not want to eat. a 2.5 gallon tank is almost the same size just taller and slightly wider. if you dont wan to spend the money i would just return him and take the didvide out of the current bowl thing and just take care of the one better. but SEROUISLY a bowl that small NEEDS to be water changed at LEAST everyother day or everyday for the betta to be healthy.

not to sound mean or anything but i would even do research on the betta even though when someone sees a betta they think hey lets throw it a jar with a plant in it and let it eat the plant only and never change the water or feed it food. and it ends up dying in a week. but bettas are just hardy there not easy ive been breeding bettas for years now and i still have problems with them. so maybe do research before or after you return the betta to see if you still want to take care of the sickly one or not and to keep the other one alive.