Luxusburger built an inverted aquarium for his fish. It gives the fish an opportunity to see the world above, and we can see the fish really well! The secret is the Shop-Vac's ability to suck all the air out. It's same idea behind koi domes, which are pre-made and float on the water. There are also ready-made fixed spheres. Or you could just install an upside-down aquarium that you already have.