Although you may need more bio-filtration, a major clue to your green water was contained in your original post..."a lot of fish". Sufficient biofiltration will take care of any Ammonia and NitrIte problems, but the end result is NitrAte which is basically food for any aquatic plants. If you don't have a sufficient number of plants, Nature will supply an abundance of mini-plants (Algae). Frequent 30% water changes will help along with reducing the amount and frequency of feeding, but the ultimate solution is to reduce your fish population or enlarge your pond.
Sorry, but there is no easy answer to this problem
