It's used to prevent winterkill in a clients pond, his pond is shallow enough that it isn't needed during the summer. During the winter it runs 24/7.

It is this system:

http://www.vertexwaterfeatures.com/sites/default/files/Air-5-XL2_0.pdf


www.hoosierpondpros.com

[Linked Image from lh6.ggpht.com]
http://www.pondboss.com/subscribe.asp?c=4
3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).