I lost the directions that came with my ecosystem. I remember they said to add chaeto after one week, but shouldn't that be determined by my parameters?
You'll want to add cheato when your cycle is complete. Cheato 'feeds' on nitrates and phosphates. If you don't have either in your tank then you have no real need for it. And, it probably won't survive. The nitrates won't be present until the bacteria colonizes to break ammonia down to nitrites then nitrites to nitrates. Then you'll have 'food' for the cheato.