Your problem with green water may have to do with you constantly changing the water. If I have it right, and I've only been "ponding" for 2 years, the beneficial bacteria (which will eat up the algae cells) is growing in your pond. When you swap out a lot of water at a time, you could be removing all or most of the good stuff, and replacing it with more of the cells that will grow algae. I know this sounds crazy, but try leaving the green water and fountain and lilies alone for a month, if you can handle that. Let the water "cycle", beneficial bacteria start to grow, and see if your green water clears up on it's own. Or, better yet, find a beneficial bacteria product at your aquarium store or pet store, or someplace other than Wal-Mart. they sell it for aquariums for the same purpose - to get rid of the algae, and it's safe for fish and plants. I use a product in the spring called "Pond Perfect". Nope, I don't sell it, but it helps boost the good bacteria quicker, once the water is warm (over 50 degree and going up, not swinging back and forth) and that will get rid of your bacteria. Other than that, figure out a way to run water through some quilt batting or something to catch the small algae cells. If you can run your pump into a laundry basket with quilt batting in it, that will catch the green stuff, and once you get rid of the green, put the pump back on the statue fountain.
Often people drain their water, and refill with "clear" water, only to have algae start back up right away. The key is to let the good bacteria build up and help you out. You can't see it, but once the weather warms the water up, it's growing. The key is to get it growing faster than the algae cells. Once you see the green water going away, you know the beneficial bacteria is overriding the algae, and you're on your way to clear water! Then, just top off the water when/if needed, don't clean the bottom or drain water out. Good bacteria grows in the layer of silt at the bottom of the ponds often, so let it stay, as long as it's not thick layer of leaves or something that is rotting.
Good luck!
