Why do my goldfish keep dying?

I just bring them home float the bag in water for 15 mins transfer them, put smooth pebbles, feed them flakes, and use filter water. So why are they dying? Is it because the filter water from the fridge is bad? I also used treatment for the water. They like swim happily for a while then like sit on the bottom of the tank and die. I got no filter but i have an air pump. I used a soccer ball sized fishbowl for one and a small tank for the other. I need help. I knoe i'm typing a lot but i could use the best help possible. any ideas?