If you look very carefully you'll see that there's a frog inside the coconut here, sticking its little nose out, while another one can be seen on the right.

As you see, this tank is not perfectly algae-free, nor do I want it to be. It has a healthy amount of non-aggresive algae, which the fish love to nibble on. I'm imitating a natural environment here, and algae are part of the picture.
That's my story and I'm sticking to it!