I also put a bit of sugar and a tiny bit of lettuce in the water for nutrients for the rotifiers
(The sugar is for rotifiers and amoebas and other critters the lettuce is just for the rotifiers and things like tardigrades)
I just made a small ecosystem in a gatorade cap for the microbes I'm taking care of; The one in the Gatorade cap is like a wet tropical biome and I'm using it to keep creatures like amoebas , rotifiers , white blood cells (thanks alot papercuts) , etc.