I've read that fish don't see red light, so it is a good way to observe nocturnal fish. I'm in the very early planning phase of a new tank. One of the fish I'm considering is Kuhli Loaches. I'm wondering if I made a cave, with an open side up to the glass, then put a red film over the outside of the glass, if I'd be able to watch them while they were in their cave during the day. Does any one have any input on whether or not this would work?