One short-term solution is to use All Clear Powder .Keep in mind that this will not fix the problem for the long term. Green filamentous algae are in fact also aquatic plants, but with a simple structure. However, they can proliferate enormously and bind large amounts of nutrients in the process. Long-term solution is to add more marsh plants and water lilies: cover the water surface 30-40% with floating plants. The aquatic plants absorb the nutrients, which will reduce algae growth. Make sure the total hardness (GH value) of the water is at least 12 °DH. Remove string algae from the pond regularly and as much as possible. As the plant stock grows and increases in size, the growth of filamentous algae will decrease: the primary growth of these algae will be taken over by the growth of aquatic plants over time. By purchasing a T-Flow Tronic, an electric thread and slime algae controller, you are guaranteed a long-term solution.