Your Chaeto may be Iron deficient. Photosynthesis is carried out within cell bodies know as chloroplasts. Iron is utilized in the electron transport chain within the chloroplasts and therefore required by photosynthetic organisms for continued functioning and health. In effect, the availability of iron becomes the limiting factor in the rate of photosynthesis, and hence the rate of nutrient uptake and growth. I dose Ferrion Iron Supplement from Brightwell Aquatics. About 2 ml. per 50 gallons once a week to keep my chaeto in good health. Chaeto will deplete your system of Iron in time.