Actually, if the air pump is broken, the fish cannot go without air for more than a day. Have you tried cleaning the pump. Remove it from the tank and then take the filter and the sponge out of the back of the pump. Discard the filter screen and replace it. It's a good idea to keep a few screens and sponges in reserve. Rinse the sponge thoroughly. If it's too dirty, then replace it. Always check the air tubes so that if the pump does break, you can replace it within a day.