I used to have a beta fish (named Ivan) who was completely awesome. He always swam around the tank, made his little bubble nests, ate his food. I kept him in a 3 gallon tank with a filter, a light, and both living and plastic plants, with naturally colored gravel. He never hid when someone came into the room or turned on the light. I also moved him several times (going to and from college in the next state over), but he did not seem to mind, as after a day he'd be back to making his bubbles and normal behavior. I changed 50% of his water once every two weeks, and I didn't really worry about nitrate or temperature, as he was thriving. He died after 3 years.
I recently got another beta (Comrade, the communist fish.) and put him in the same tank (after cleaning and new water, gravel, and plants, of course!). This beta does nothing but hide in the plants and ALWAYS has his fins puffed up at me. I never see him eat, but he must because it's been three weeks and he's still alive. I started to check temperature and nitirate and ammonia, and they are all normal, and the temp is 79 degrees F. The fish is pissed off and mean looking all the time, and he does not make his happy little bubble nests. I feed him 3 little balls of food 3 times a day.
What am I missing to make him happy? Was he abused or something in the pet store?