Total specs, in hopes that someone thinks it's a nitrate problem and has an
answer. BTW, the nitrate-limited thread I was referring to is at:

http://groups.google.com/groups?q=la...aol.com&rnum=1

Anyway, 500 gallon pond, full sun, lots of plants mediocre circulation (for
now, will be improved).

nitrate = 0
ammonia = 0
pH = about 8.5 (tap water = 8.0)
KH = 180 (tap = 180)
GH = 250 (tap = 120)

....lots of rocks in pond, btw.

K in message referred to Potassium, in my case K sulfate. Sigh. Any ideas?

Mike, what are your test results?
Heather, have you measured KH and/or GH? After I checked my KH and found
a really low amount, I've been adding baking soda over a two week
period. After just a few cups of baking soda, all of the pond plants
started growing and greening up.
Mike, is the "K" potash? I was planning to add potash to our pond, but
am holding off now until I can get the KH up to a better level.
--
Zk (sig. compliments of BV)