Charlie:

Look at the specs for you diffusers. I don't know which ones you used, the ones that are rated at 0.5-4.5 SCFM or the ones at 1.0-8.0 SCFM each. But keep an eye on the Who's up for a road trip to N. Central Indiana thread. Ted tested that same compressor on a diffuser at different depths in my pond and the results will be suprising - you too RC51!

Can you find a volume/pressure curve for that particular compressor? I looked for one and couldn't find one.

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).