I've had my betta only for about a few months. He goes through these phases I think, he was fine the first couple of months, then he started to get really sick. He wasn't moving, barely breathing, wouldn't eat, and he had trouble even holding his back end down. It would just float along with the water. I cleaned his tank (I do this once a week) and I decided to change his location. He used to be downstairs, but it stays cooler downstairs, so I moved him up in my room where I always have it nice and warm, so his water would warm up. After a few days he came around and was back to normal.
Now, maybe a month and a half later, it's going on again. About a week ago at this time he was fine, swimming around, getting excited to eat, everything, but like a day and a half later, he had stopped eating and didn't do much. Now most of the time he is laying on the bottom of his tank on the rocks. Every once in a while he gets these crazy spells where he just flies around the tank in random movements, sometimes nosediving into the rocks, he splashes around. That normally lasts about 1 minute, then he's right back to laying on the bottom. He is losing his color, and I looked to one side and there is a dark spot. I don't know what it is. My first thought was a bruise, but I don't know if fish can get bruises. He also has a black spot near his head as well. His body color is a whitish with a tint of pinkish purple, the that tint has faded away almost completely now. There is no spot on his other side. He had a tree in his tank that I just removed in case it's releasing toxins. His rocks are the marble stones.
I really have no idea what is going on. Can anyone help?