Information provided by TetraPond
One of the most important factors to keep water conditions suitable for fish is the amount of 'air' (oxygen) in the water. As pond owners, we regularly fight an uphill battle to keep levels at their optimum to achieve aquatic balance.
Oxygen levels fluctuate on a daily basis, especially when fish are active in the summer. The hotter the water is, the less oxygen there is available in the water and, due to increase activity, the fish need more oxygen.
Aerating water is achieved by disrupting the surface and increasing the area where oxygen and carbon dioxide can be exchanged. Among the best methods are:
Not to mention, some fish love the current and bubbles produced by water entering the pond. Perhaps it's a fish's version of a therapeutic massage!