Bubble Tube

There has been a massive die-off in my fish-tank. The population has gone from about 20 to 4. We thought a disease carried in by a new fish we purchased caused it, but we couldn't be sure. After several water changes fish were still dying. No fish has died for about a week so we think the deaths have stopped (cross your fingers).

My mom noticed that the old bubbler we had in the tank was disintegrating, so we changed it out just to make sure it wasn't the cause. This is the tube that pumps water from the bubbler. Here is an above view of the bubbles hitting the surface of the water.