Hello...
I have kept 2 very large chunks in my garbage can "skippy-type" filters for the last three years, 24/7/365, and only experience string algae in places that get alot of air movement/oxygenation, (my small creek and waterfall)... Prior to that I got string all thru my pond and it was a pain keeping it collected and out of the pond.. Have to admit all my marginals and pondside plants that creep into the pond around the perimeter have matured much over the years, and definitely suck up nutrients, but for now I am keeping the barley straw in the filters... It is very cheap for a bale of it at the local feed store and doesn't require any maintenance, except to fill the plastic onion bags every year... Tried Koi-Clay but didn't see much effect... Have heard it works for some, however...
I've never tried the Algae-Fix or any other of the soluble chemical products...
Take Care...
Dave