I didn't know that clay would bind the Iron to cut off nutrient to the String
Algae. My experience with clay and SA was that the clay bond to the SA and
block off the light. The SA would disappear after a few days.

You don't need Koi clay. I used clay marketed as plasticizer for thin set
mortar at OSH before. I always used it to clarify my aquarium, until I ran
out. My latest accidental discovery is that Koi shifting through 5 bag of
Special Kitty litter have the same effect.

jbjrfan wrote:

Thanks for the tip as I have been fighting this string for years and tried
lots of stuff that only seems to keep it from getting rampant and not
killing it I will go out and buy some and give it a try if it works and
doesn't kill my plants its the best tip ever for me :-)