The paper didn't stick and light seeped through. We had to cover the top,too, so we used a cloth. The cloth kept falling into the tank and germs that were on the cloth got into the tank. This also worried us because the cloth had been washed with bleach. Water also soaked into the cloth from the tank and seeped out.
Dead eggs can be a problem, too.
If they are not removed from the tank, they can spread diseases. To get rid of the dead eggs you can suck them up with a turkey baster. You can tell they're dead when they turn whitish, and when you blow at them with the turkey baster they float up. Live eggs are a clear yellowish color. Remember to keep your hands and tools clean when you test for dead eggs.