My ecosystem can be made using:

1 bag of daphnia
1 stem of elodea crispa
1 bag of cyclops
1 jar
A few bits of algae
Duckweed
Gravel

1. Put the gravel on the bottom of the jar.
2. Put the bottom of the crispa stem in the gravel.
3. Fill it with water.
4. Add blanketweed and duckweed.
5. Add the cyclops and daphnia.

This ecosystem now can be sealed with the lid of the jar. The only thing this ecosystem needs now is light. This experiment is good for first grade teachers.