On Sat, 21 Aug 2010 07:51:56 EDT, Jim Elbrecht wrote:

The only chemicals I've ever used is some Algaecide on occasion to
keep the string algae down to where the snails can eat it.

[also]
Jim
[In NY where it has been a very hot- very dry summer]

There is your culprit. Algaecide. Some plants are very sensitive to it. pH
and KH can also make them more or less so, why sometimes it bothers them
and sometimes it doesn't... and why it bothers some without bothering
others.

I had WH in a floating basket and the koi finally pulled it all out, but it
is doing great floating free now so I pulled the basket out weeks ago. Nice
to have it in the pond again. It has never grown that well in the lily
pond, but this year, where I have some that the roots are in contact with
soil they are doing fairly well. Need all the baby/egg saving plants in
there as wakins are sure caviar eaters. Only 3 babies of size brave enough
to join the adult group have shown up recently. I do have an amazing mat of
watercress hiding some smaller ones. ~ jan
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Zone 7a, SE Washington State
Ponds: www.jjspond.us