David Livingston wrote:The plants I suggested will eventually do that but it will take time
David
I agree, having a variety of pond plants should help. The algae feeds off the excess nutrients released by the fish and the decaying leaves. Pond plants will soak up these nutrients, denying the algae. Like David says, it will take time. However, I think it is worth it, as it's a permanent solution, unlike say dredging the pond twice a year.
From
Gaia's Garden, Toby Hemenway suggests the following plants as being effective at purifying water: Bulrush (Scirpus validus), Canna lily (Canna spp.), Cattail (Typha spp.), Soft rush (Juncus effusus), and Reed canary grass (Phragmites communis). He also says Reed canary grass is on some invasive species lists, so check before introducing. Note: this list is in his section on graywater wetlands, but I believe the principle applies to static ponds as well.