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 [email protected]