I also have four brine shrimp who live in a biosphere that is completely sealed. Oxygen is provided by algae. All I need to do is make sure it gets sunlight every day so that the algae will grow. Brine shrimp are the creatures they sold as Sea Monkeys in the back of old comic books when I was a kid. Unfortunately, these shrimp never wear a crown and carry a trident while riding around in a chariot pulled by sea horses.