Is the tank in a room with natural light?
I had a big algae problem that was choking my plants out. Mostly black beard. Hydrogen peroxide only helped a little, but wasn't killing it.
Now I keep the light off except when I'm watching them (the tank is in my sun room and I keep the front blinds shut) and I added two black nitrate snails. They have eaten all the black beard algae!
Love your puffer