An algae bloom is normal when the pond is brand new. If you are patient and the pond is properly balanced, you may not have one, but don't be dismayed if you do. If it lasts more than a week and you absolutely MUST be rid of it because your mother in law is coming to visit tomorrow, there is an emergency procedure you can do right this minute and your pond will be clear by tomorrow. This is not a permanent fixture in your pond, nor is it the universal panacea for algae, but it will get that pond clear so you can show off your brand new handiwork to your visitors.
Do not use any of the algaecides that are available commercially. Most of them severely decrease the oxygen level in the pond and that will kill the fish. Remember that anything that will kill algae will kill other plants. Fish will tolerate green water--they will not tolerate toxic (albeit clear) water. If you have consistently green water use more submerged vegetation (Anacharis) and make sure at least 50% of the water surface is covered with floating vegetation to provide shade. This floating vegetation can be water lilies, water hyacinths, water poppies, etc. And stop feeding those goldfish.
If you must get rid of your green water fast use a temporary mechanical filter. I use a large black pot that a plant has come in--10" or bigger I also put a few more holes in it than just the one on the bottom. Be sure the holes are on the bottom of the pot or whatever container you use. I put 2 inches of foam rubber in the bottom of the pot and suspend it over the surface of the water. I usually use a lawn chair or upturned 5 gallon bucket. Next I run the hose from the pump over the top of the pot so the water runs through the foam rubber. I hold it down with a brick. This makeshift filter looks awful and must be cleaned every 2 hours or so, but it will clear up your pond in a day or two for the cost of the foam rubber. You can tell when the foam rubber has to be taken out and cleaned because the water will start running over the top of the pot. The finer the foam, the more often you must clean it, but the faster your pond will get clear. You must keep an eye on this jerry-rigged set up and continue to clean the foam rubber or your pond will not clear up.
