You running ULNS? your tank has 0 hair algae? If your tank is so clean that chaeto won't survive then you don't need chaeto. Chaeto is a way of nutrient export, you don't really add nutrients for growing chaeto, it should have enough just from your fish pooping and excess food you feed your corals and fishes with.
Chaeto dying has more to do with the light spectrum you use on it.