Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
do not mean oxygen.
Air pumps are pumping pretty close to 80% N and 20% O and a trace of other things.
These gases do not really enter the water unless the tank is WAY deeper than any private aquarium I have seen. (Perhaps the 2 story high public aquariums...)
Air pumps "add oxygen" because the bubbles drag some water with them, from the bottom, rising to the surface. Water from the bottom may be low in O2 and high in CO2 (in a non-planted tank). This water sheets across the top, and the rippling means more surface contact with the air. When in contact with the air the water gives up the excess CO2 and picks up more O. Then this water sinks because more water is rising to takes its place.
To improve the oxygen level without an air pump is a piece of cake:
ANYTHING that creates better water circulation will help, and the best help is a water pump (power head, Koralia style or filter) that creates more surface movement.
In ponds and small lakes they will put a pump in the water that shoots the water from the bottom vertically, perhaps to fountain, or perhaps simply to ripple and flow across the top of the lake. This is called a flume. HIGHLY effective way to oxygenate the lake water.
Other ways to increase to contact between air and water is to spread out the water such as a stream or water fall. Not very practical indoors, though.
Many Loaches and Cats, and quite a few other fish come from shallow, fast moving water that is relatively cool. Hillstream Loaches being an extreme example. White Cloud Minnows, some Danios, certain Plecos, are some other fish from this sort of setting.
These fish may have poor oxygen coping ability and require very high oxygen levels in the tank.
Keep the water cooler. Cool water holds more oxygen. Do not mix warm water fish and cool water fish.
Keep the water moving. 20x the tank volume per hour is a minimum for these types of fish. This much water movement can be from a combination of filter and power heads. The surface should ripple pretty well.
Keep these fish in a wide, long, but shallow tank. Not a particularly deep tank unless you make a really good circulation system. Tanks like 'Long' and 'Breeder' are generally better than 'Show' or 'Tall'.