I've used the UV systems, which are not as effective as I thought they
would
be. What was the answer, in the end, is to pump the water up a level to
another "pond" which was a 1 metre square hole filled with fine gravel,
into which were planted bullrushes, then let the water run back down (over
an ornamental rockery slope planted with alpines and hostas). The
bullrushes "eat" whatever it is that blanketweed likes. My
biology/chemistry are not up to knowing exactly what, but I believe it's
somthing to do with nitrogen balance. Also my Koi Carp "Frank" became
pregnant, so they must like it too. He became known as Frances.

HTH




Interesting. The UV system seems to work well on all but the sunniest and
warmest period. I did check the lamps were OK and clean at the beginning of
the season and all looks well. Maybe we should get some more plants in the
ponds next year.