UV doesn't work on string algae or substrate (grows on rocks) algae
unfortunately.
This is just a total guess but
the dead UV zapped suspended algae may be feeding the string and substrate
algae.
You could try power washing the stream, sending the waste water away from the
pond.
Or sending the UV zapped water to a settling chamber and/or mechanical filter
which sounds like reorganizing your system and I'm not sure how effective that
would be. (Wait for UV users to chime in here... ;-)


kathy :-)
A HREF="http://www.onceuponapond.com/"Once upon a pond/A