I had a tank that had a terrible green water problem. It was a planted shell dweller tank with pretty high lighting. For the first year, nothing worked. I tried water changes, duckweed, adding Seachem Flourish Excel, turning off the lights for days. Still the water was deep green. I couldn't see fish or plants or anything. Probably the most frustrating tank I've ever had. The kind that just makes you want to tear it down and swear off plants forever.
However, after a few months of just leaving the tank alone with small water changes, something changed in the tank that started favoring the plants. I don't know what it was, maybe some nutrient was limiting the plants growth. But the giant vallisneria took off for the surface of the tank, and the algae cleared almost literally overnight. Now it is one of my favorite tanks.
Pretty amazing to see, really. The lesson I learned is that patience is key to aquariums, especially when dealing with plants. The more changes you make, the longer it takes for your tank to find its own equilibrium.
If you aren't keeping plants in the tank, I would recommend just decreasing the light a ton. If it is a two bulb fixture, unscrew one. There is no need for high lighting in a front tank, as they are adapted to the low light of the deep parts of the lake. Bright lighting can actually make them very reclusive, as well as cause the algae blooms. Remove the lights, and don't succumb to the urge to do huge water changes, as that has never worked in my experience. Small, regular water changes, and the problem will eventually go away.
