I had Sea Monkeys when I was younger. I don't know much their proper care though as I just had the children's kits. There's lots of information on brine shrimp care online. Sea Monkey is a marketing term, like teddy bear hamster.
The green powder you feed them is dried spirulina. You can buy it online and it's cheaper than buying the official little sachets.
You can start out with a kit like this but if you want to keep them well you'll want to upgrade to 5 or 10 gallon tank eventually. The kit will be easier to start out with because the water conditioner contains just the right amount of salt etc for the tank, so you don't need to calculate anything. When you get a larger tank you'll have to work out how to get the water right for them.
Edited by daisy~, 01 October 2021 - 10:15 PM.