Aeration

It is not true that we can always and at all times double the proper number of fish in a tank just because aeration is provided. The utmost that the aeration can do is to keep the water at full oxygen content and to help eliminate harmful carbon dioxide gas. In fact, it can easily fail to do even that if the water temperature is raised thus automatically lowering the oxygen content. Aeration will also fail to keep the water at full oxygen content too, if the carbon dioxide content is raised by dirt or other matter fouling the tank by the fish present being too numerous, too big or too fast swimming.

Aeration does help but to credit it with doubling the fish capacity of a tank is going too far. If a tank will satisfactorily hold twenty five fish without aeration, then thirty two to thirty seven is the maximum when constant aeration is provided. In this case, thirty to forty per cent increase in the amount of fish is considered reasonable enough when aeration exists.