Green-water in a preformed pond?

We have terrible trouble with string algae/green water in our small pond. We have used two rounds of algaecide so far this year and we put the barley in regularly. We really don’t have any life in the pond (except for two remarkable goldfish that someone put in that pond last year.. not koi, little goldfish.) Toads, however, really like to mate in that pond. We are constantly pulling strings of toad eggs out of the filter… so we don’t want to use anything that could be harmful to wildlife. We also bought some dark dye for the water, thinking that it would help to filter sunlight.

We’re having a wedding reception for a family member here this weekend, and I really wish we could get rid of that murky water in time. Any tips??