You are correct and I learned a little something today. I knew they would swim towards a light source, but didn't really think about them doing that in the fish tank since the entire tank is lit up. Turned off powerheads and pumps and sure enough, right at the top. I guess there is some advantage then to being able to leave everything on. Off to learn some more on this subject....To quote one of the brine shrimp hatching pages... "The shrimp are phototropic and will swim toward the light, conveniently gathering themselves together." This pretty much sums up my experience. LOL That's also why a lot of the hatcheries are dark and the shrimp are forced to swim to a light source where the collection area is. Here's one of the hatcheries I have. There are a gazillion bbs swimming in that collection cup right now. They swim from the dark hatchery box up through a hole into the cup where they detect light. I have another inverted bottle hatchery where most of the bottle is blacked out except an area at the bottom so they swim to that area where the light is and I siphon them off. So in my tank with the pumps/powerheads off they just swim to the surface toward my light.