I thought that I'd chip in here on this. We just built a 7000 gallon pond
with two waterfalls, one that splashes a lot (but not much leaves the pond)
with an upper pond of 8x10 ft (more or less) and then a ledge waterfall to
a lower pond that is 13.5' x 14.5'. It appears that I'm losing about an
inch every 3-4 days which is about 172 gallons.

Does this rate seem reasonable?

Yes, that sounds very reasonable. ~ jan

Zone 7a from the desert of E.Washington where our humidity is also very
low.
See my ponds thru the seasons and/or my filter design:
http://users.owt.com/jjspond/

~Keep 'em Defrosted~
Tri-Cities, WA Zone 7a
To e-mail see website