I've been reading an older book called "Management of Lakes and Ponds" by George Bennett (2nd edition 1970, pg 47) and they mention a hydraulic air gun to raise water from under the thermocline up to the surface. The device is supposed to be quite efficient but unfortunately there are no photo's or line drawings of the device. This device may pre-date the aerators we have available today but I was interested if anybody has any details about the construction of this device.

I would guess that it would be an air source inside of a vertical pipe. The rising air would lift water, similar to the action of a bottom aerator.

i have come across a few clients with a system from a company called Grovac? THey are a stainless or galvanized tube with a spike on the bottom. the airline runs in and attaches to a tube running through the larger tube. the smaller tube has several holes in it. In both cases the system was not doing much and I replaced the tubes with Mix Air diffusers which made a substantial difference with water movement and oxygen levels at the bottom. The diffusers are designed for wastewater treatment and have little back pressure and produce extremely small bubbles. They are also easily suspended off the bottom and have more surface area than disks or bladders. THey have an open spiral design wich allows water to pass up and thru the coils instead of out and around if you can imagine. I would be happy to send anyone some literature and prices.
Robert B fishmgr@hotmail.com

Robert, though I'm not ready yet I hope to be in apx. a year. If I don't respond to this now I'll forget. Please send me info.
Thanks
rkswaim@hotmail.com