Spray Bar

From Koipedia

A Spray Bar is a very simple and inexpensive way to aerate your koi pond. Generally, you create a spray bar out of a length of 2" PVC tubing, drill 1/2" size holes every inch along the tube, position and attach the tube above your pond or above pond level filter tank, and attach the output from your pump to the tube so that water sprays from the spray bar.