Ray, all of my devices have been on this and other forums over the years I just forget when.
This is the brine shrimp hatchery which I made decades ago and still use it every day.
You put the eggs on the right, dark side, then in a day you cover that side and slide open the door that covers a hole to the lighter side. In about 10 minutes all the shrimp swim to the brighter side and the shells stay on the right side. I slide down the door and open the valve, just the shrimp come out. Then I drain the thing and put in a new batch of eggs.
My fish get new born brine every day.