The water in the tank doesn't need to have a boiling action for good gas exchange. The surface just needs movement. Check the filter and if it's moving the water smoothly, then that's all the tank needs. An air stone does very little to aerate the tank. If you want more surface movement, then get a small air pump and attach enough plastic tubing to reach the bottom of the tank. You can secure it to the side with a small suction cup and plug in the pump. You have large bubbles that will really move the water surface. There are small valves you can attach to the tubing, so you can raise or lower the amount of air the goes through the tube, too.
"Fear not, my young apprentice. Just change the tank water."