Just as air quality will help keep people healthy so 'air' and quality of that 'air' in water will help keep fish healthy. I find this area fascinating and find that the industry is really starting to mature. Many of the links l include can be used for aerating water and/or the air we breathe. You'll have to forgive me if I link to stuff that will take you off to other lands and places that are not 100% related. Just enjoy the ride..

Balboa Instruments-Here's a unique product that uses ozone to naturally disinfect water.

Biodome de Montreal-Info on a denitrification system plus other information on various aquariums from Ecomat.

Fiber Optic Sensors-Can detect the amount of oxygen dissolved in the water.

Megalite-What is this porous ceramic and how does it help clean your pond?

OnSiteGas-These onsite oxygen/nitrogen generators are much cheaper than you ordering in tanks of the stuff. I think on site generation is the way of the future.

Oxygen Generating Systems-Multiple uses for onsite generation with purities 92-99% New York

Oxyguard-This probe can measure the amount of oxygen in the water. Except for cleaning it requires no maintenance.

Oxygen Cones-I don't fully understand how these work except they have a 95% efficiency rating and are to be used while putting water back into the aquaculture system.

VSA Oxygen Generators-Article on these VSA generators produced in Calgary, Alberta.