I was going to suggest fruit tree bird netting, but then I read your post about the parrot. You could use eggcrate to cover the tank. But even that's really no match for a parrot's beak. fwiw, I went to eggcrate after losing too many anthias. I've come to realize that eggcrate can in fact focus the light entering the squares, but much is sacrificed in terms of area coverage. I just switched one of my 125's to a double layer of fruit tree bird netting and it makes a big difference. The double layer alternates the netting mesh so the available openings are very small. hth