I will admit that I didn't do as much research as I should have when I first got my betta (Charles), but I didn't have any problems with him until the weather changed and the room temperature dropped.
I noticed that he was lethargic and, until I got him a bigger tank with a light, I kept my desk lamp on his tank to make the water warmer. I got him a new tank last weekend and since it's only a 2.5 gallon tank, the light that it came with was sufficient to heat it up to about 74 degrees F. I know that the water should ideally be warmer, but the PetSmart I went to didn't have heaters for tanks under 5 gallons so I wasn't able to get one then. I've got a little thermometer to make sure the water stays at least above 72 degrees.
Anyway, I noticed that in his new tank, he still wasn't actively swimming and I haven't seen any evidence that he's eaten in the last week. He kept staying up at the top of the tank, in a corner, and barely moving. By this Saturday, he was bleeding from his mouth. I did the research that I should have done much earlier, and found ammonia poisoning.
I did a 100% water change and bought ammonia testing strips, though after doing my research and talking to the employees at PetSmart, I had concluded that no matter what I did, my fish was probably too far gone to be saved. Knowing this, I continued to keep his light and filter on, test the water and feed him. He didn't even seem interested in the food, so I would take it out of the water so that it wouldn't decay and bring the ammonia levels back up.
I've been fully expecting him to die since Saturday, and quite a few times it looks like he has. Sometimes he floats on his side at the top of the tank for a few minutes, and then swims back to his corner. I don't know what's going on with him, as he's not eating either so no matter what, if this continues he will end up dying.
Does anyone know what's going on with Charles? I don't want him to suffer, and I feel bad that I didn't do the research and know about everything ahead of time.