I have 3 Zebra Danios, 4 Leopard Longfin Danios, 2 Neon Tetras, 2 Glass Shrimp, and 1 Cory Cat in my 20 gallon tank. When I turn the light off, my danio fish freak out; swimming around franticly bouncing off the sides of the tank. It's not like it's completely dark, there is small amounts of light from the night light in the bathroom nearby. Is this normal for these fish to do this? Should I leave my light on for them, or turn it off for a while at night?