Even so they require much less to survive compared to plants, there are still basic care instructions you should adhere to. For one, you need to periodically pull them out and squeeze them. Then you should regularly turn them so they're not just on one side exposed to light. In nature, they're constantly tumbling around for that round shape. Lastly, if you supplement excel or glut, I believe too much will kill them. I don't even use excel in the same tank I keep my marimo in.