Good aeration is necessary for nitrification and for fish growth. Aeration adds oxygen to water, removes carbon dioxide and other bad gases (methane, hydrogen sulfide)
from water. Aeration also helps mix water, adds movement to water. If air diffusers are placed on top of a bottom drain, the convection movement they create can draw dirt from the floor towards the drains.
If a pump fails for some reason, fish will not die because aeration still keeps the water clean for a while. For this reason, you can have 1.5 times more fish in your
pond than if you didn’t have aeration. Just remember to connect aeration to a different outlet than the pump.
If your pond has no bottom drain, not to worry. You can always add a retro drain or extend the pump suction end to the center of the pond and add a filter at the bottom
(availabe at azponds). Then put a soaker hose around the drain, weigh it down with rocks. Connect the soaker hose to an airpump. Viola! you have a bottom drain with air diffuser.
There are two types of airpumps - cheaper diagphragm type (example: Danner or Pondmaster AP series) and the more expensive linear type (example: Hakko)
From our experience, the cheaper diaphragm type Pondmaster air pump worked better and lasted longer than linear type Hakko air pump, even at depths
of 8.5 feet and a distance of 60 feet from the pond !Only drawback of a diaphragm type air pump is that after working for 8 - 12 months continuously, the diaphragm breaks down. So, you need to buy a repair kit ($8). But even after
replacing 10 times, diaphragm type is still cheaper than the linear type air pump.