String Algae & Kitty Litter ?

I lost the original post-- Would you be kind enough to tell me how much
you used, where in pond: and how often you added it? My pond is about
1800 to 2000 gallons, with 20 lg shebunkins and goldfish. I have a sm. (
50 gal.) veggie filter at the top of the falls. It is filled with
lettuce and hyacinths. There is an 7 foot long spillway with 2 small
drops, Then water then flows over the bottom lg basin shaped rock and
into the pond. I have string algae growing over the bottom rock,
stranding into the pond. Hand removal, isn't enough. The stuff seems to
grow like a weed.
Thank you for any help.
Bette, in Central OH