Hello efface. There is a very extreme method of algae control, but I hesitate recommending it until all other means have been exhausted. Have you tried just planting more stem plants in the tank? I used to have an algae problem, but I planted the following: Water Sprite, Water Wisteria, Rotala, Ludwigia and Pennywort in my tanks.
It took some time, but with frequent and large water changes and plant growth, the algae just died back. I haven't had a problem since.
Now, the extreme method is to use Cidex. It's an undustrial form of carbon that's toxic to the more primitive plants like algae. It contain 2.4 percent "Gluteraldehyde". The problem with using it, is the stuff can also be toxic to ferns, mosses and some varieties of Vallisneria.
I used Cidex for a few weeks some time ago in one of my tanks and it killed the algae and my Corkscrew Vals and damaged my Java fern and Singapore moss. I stopped dosing, but the ferns and mosses have come back a little differently. If you decide to look into Cidex, make sure if the activator comes with the order, throw the activator away.