well I use a bacteria additive all season long which helps and mine has
died
back a lot in the last few days, if not completely gone - if you haven't
tried that it might be worth a try
Gale :~)

I'm in Southern Ontario. I never really has a String Algae problem until
the
end of last summer. My lilies were doing fairly well, but have slowed down
a
bit. They may need some plant spikes.

What's the bacteria you mentioned?

As George mentioned, there are many brands of Bacteria additives
available -I have used Bacta Pur Klear for 8 yrs now - a 1 liter bottle does
my ~1000 gal pond for the season at a rate of 1.5 - 2 oz/wk until Sept
Lilies - I have read over and over here how some people have profuse
flowering of their lilies without fertilizer and decided to try it one
year - I only got 1 or 2 flowers open at the same time w/ small lily pads
and went back to my pond tabs the next year - 2 to a pot every 6 to 8 wks I
am currently at ~ 40% surface coverage with pads and today have 4 flowers
open (first ones)
Good Luck Gale :~)