A few more details would be a good thing but I can give you some general advice. How many fish and what kind?

Well here is my opinion. HAVE PATIENCE. Stop throwing chemicals at your pond and leave the water alone.. I know you don't have patience but this is a cycle thing. It WILL be green in 2 weeks everytime you refill it. So stop refilling it. Allow it to cycle. Your pond could have to much of a bio load on it with all the tadpoles and fish. I don't know how many you have, so I am just generalizing.
How have you ever maintained it for 2 years? Have you been refilling the pond every 2 weeks for that amount of time? I seriously hope not. The algea will feed the tadpoles and the fish, unless you have way too many. How often do you feed them? You don't say that part. Some people feed their fish 3 times a day, I rarely feed mine. I don't have many though, maybe a dozen in a 1000 gallon pond.

I am sorry if this isn't the answer you wanted, it is my experience and opinion though.

okpondlady is absolutely right - you need to let your pond cycle. One of my two ponds took 1 month to clear up this year, but it did clear up.

marni, I thought your posting was sort of funny. LOL

You seem to think that you can order Mother Nature around and get her to do what you want. She will give you green water forever unless you do what She wants.

So grow up and work with Nature and not against Her.

Marni:
waiting is hard to do. I have been comtemplating barley straw for the first time, but after 4 LONG weeks of strong pea soup I can see clearing the last 2 days. Ditto the leave it alone advice. Big water changes will feed the bloom.

marni,
I have thought long and hard about this thread and although I know that I will make an enemy, I must tell you that you did not deserve the message from catfishsam. I hope their rudeness doesn't keep you from posting again. It is a shame that from time to time we see this kind of thing. It keeps others from posting because they do not want to be embarrassed or belittled.
bugsb

Here is a link that might be useful: My pond the way it was before the freeze.

I agree with the word patience.Cant over emphasize that word enough. I had pea soup minus the ham bones for near 5 weeks .... then it cleared in a matter of days. Emptying the pond and then refilling just gives the algae more clean water to inhabit.It takes a while for the plants, filter and mom nature to get in balance.

Couple of things...

Barley bales will work.. but with the cooler temperatures, they do not work as well as they do when the water temps are higher later in the season.. that goes with most of the chemicals on the market.. water temp will increase or decrease their working ability by the higher/lower temps.

Shade, that's a good thing... you want to have at least 2/3 of your water surface shaded by plants.. hence the water lily is a good choice for this. Plants that compete with the same nutrients that feeds algae are the oxygenators..anacharis/ parrot feathers/ etc. invest in one plant per square foot of "surface" water area. Submerged plants work best also. Marginals are really not that much of a work horse in the pond.. they might provide some shade, but they don't compete with the nutrients in the water as much as the other already mentioned plants.

Changing out your water.. no more than a 1/3 water change at any time... everytime that you change your water, the water breaks down and encourages algae bloom... rainfall/ snow melt can all add to algae bloom. Your pond needs time to establish an environment that will help fight algae. Some algae is good for the pond. Did you want the pristine pond? Because you have fish there is no way that you are going to have a pristine pond.. cause the algaecides that kill off algae will also kill off your plants and fish. Therefore the only thing you can do is control algae... it is an ongoing process, it's like weeding your garden, you don't weed it once and expect to be done. Same with algae, you don't "weed" it once and it is done. As your plants come in and provide more shade and the plants start to compete with the algae nutrients, this will also help cut down on the algae.

Don't feed your fish too often, this will make them "lazy" and they won't graze on the algae as often. Also, in the spring, before the bacterial levels in your bio filters are working at their peak (again, water temps).. feed your fish a high carbohydrate fish food.. their waste products will be easier to break down in the bio filters... if the fish are putting out too much for the filters to breakdown, it will go to feeding the algae instead. Once your bio filters are working at peak, higher temps, switch to a high protein food for your fish. goldfish don't even need to be fed.. koi, yes. But not as often as you might think, cut back to once a day, once every two days.. depending upon the size and type of fish.

Lastly, allow a less than perfect pond.. it will allow you more relaxation time by the pond. Ponds are not 100% natural environments.. they are human maintained.. (And a "real" pond is rather yucky.. I wouldn't swim or wade into a real pond.. they are sludgy and murky).

Marni:

Have you tried the barley bales? You have to look at them floating in the pond (we suspend ours behind the waterfall - they need to be placed in moving water to be most effective) and they take about three weeks to start to work but they seem to have really helped my water clarity. I'm in a different situation than you; this is the first year for my pond and here in Raleigh, NC, where things warm up fairly quickly, I had a huge algae bloom in March/April that lasted about 6 weeks with first green, then brown, pea soup water. Very frustrating. We joked that the Creature from the Black Lagoon could be lurking in there in 2 feet of water and noone would know it. We had a convergence of things that might have finally cleared our water - we added fish, an abundance of lilies, anachris, and plants at about the same time that we added a UV light so it's hard to tell exactly what specifically cleared it up. Our water is crystal clear now but our water parameters are not yet where they should be (nitrates haven't kicked in so the ammonia and nitrite levels keep yo-yoing.)

Two other thoughts: I believe that the UV lights are only effective for one year's time and need to be replaced annually. Also, I think changing out so much of your water so often will only prolong the problem and you must instead let nature achieve its equilibrium. Our local koi/watergarden club suggests a weekly water change of only 10%. I don't know where you are located but I have also read that rainfall can sometimes cause algae blooms. You said that you have covered your pond. We have been told that your pond should receive at least 6 hours of direct sunlight a day and that plants (lilies) should be providing the coverage for the water in order to have a healthy pond.

Thanks everyone for your responses! I have increased my patience limit to 5 weeks- based on others experience- so hopefully will clear up by the end of June.