Mudhole,
On ebay is a system that I have worked with personally. I still build backyard watergardens and install one of these in each pond I build. It is reliable, from MI and silent in operation. Search for KoiAir 2 on ebay.
This uses a liner air compressor along with 2 diffuser plates with a substrait barrier. Each plate has 2 EPDM membrane diffuser sticks.
4 feet depth is max for this unit. If you are deeper, look for
Shallow Water or AM10 or AM20. For deeper, look for a Vertex unit.
Look for made in the US, reliability, ease of installation and maintenance and operational cost. Goal for your small pond is to provide enough turnover to ensure even oxygen levles from top to bottom, temperatures the same from top to bottom and increase the area for beneficial bacteria to do their work.
