If you have transfer ports then that is the best place to put the air stones, but many filters do not have transfer ports especially vortex filter units.
If you have Japanese matting or Kaldnes K1 as the media then you should have the air coming from under the media. This is usually done with a ring of plastic pipe with small holes drilled in it.
Posted on Oct 3, 2005, 4:43 PM from IP address 86.128.124.147