Why do aquariums need bubble bars and stones?
They don't.
However, they do serve some purpose. Bubble bars help oxygenate the water; this is especially important for freshwater aquariums with weaker pumps. Bubble bars also cause surface agitation, reducing the growth of surface algae and aiding in surface gas exchange. However, bubble bars are largely aesthetic; every function they provide can be done more efficiently with other equipment.
By stones, I'm assuming you mean gravel. Again, this is not something that is 100% necessary, but they do serve a purpose. First, they provide a surface for nitrifying bacteria to grow on; these bacteria are essential for the long-term health of fish. They process ammonia into nitrite, and then nitrite into nitrate. Both ammonia and nitrite are toxic to fish; nitrate, not so much (though too much is still dangerous). Second, gravel helps to stabilize the pH of the tank water; the gravel acts as a buffering agent, minimizing swings in pH. You can have a bare-bottom tank (and many saltwater aquarists swear by them), but most aquarists do prefer to have gravel or sand of some type in their tanks.Tropical fish, both fresh water and saltwater need air, and not just air through the filter. Natural rivers and streams create air through the currents. Wave action in the ocean and underwater currents provide air for sea life.
Extra bubble bars and air stones help simulate these currents. In a saltwater tank, a skimmer at the top of the water simulates wave action.
Although it is important to keep an aquarium filter clean, it is even more important to provide extra air for fish and other aquarium life.
