Ok, a few weeks on and with a bit of trial & error to the pond I now know that there are many different types of algae and that the Colloidal Silver doesnt really seem to work with all of it. In our case its the stuff that gives pond water the thick almost fluro yellow / green pea soup look. We didnt have this type of algae when we started but it flourishes on fish food - something we discovered too late. We are fixing the problem naturally though so alls well that ends well (-: