After removing layers of the green algae, the next task is to kill and remove any string algae that looks like like green hair. You can do this by pouring kosher or other non-iodized salt on the algae and allow it t0 settle for at least two to three days before removing the algae.
Now you have to make sure that the algae you have removed does not grow back for a considerable amount of time. In order to do this, reduce the amount of sunlight and nutrients available to the algae and instead, add more beneficial bacteria to make it starve, which will ensure a clear pond.
After you are done with cleaning the pond, you can transfer the fish back into it. However, it is good if you drain the old water and fill the pond with fresh water which will reduce the risk of the algae growing back.